I am a first-time GM trying to run a short Dragon Age campaign. During our first game, I hid the character sheets of the NPCs and enemies from the players. Is this appropriate? Should I give the players information as to what the enemies' abilities are before the enemies' turns in battle, or exact amount of health left in combat?
Usually speaking (without going into specific systems, where it might differ) what you share with the players regarding the character sheets and information of NPCs is roughly the following:
Anything that any person would notice
These are things that anyone should understand about their current situation. Yes, the Dragon is bigger than you are. Yes, it has wings and can probably fly. It has tough looking scales. According to the stories, it will breathe fire, too.
The soldier is wearing armor and a large sword. His cohort is wearing a massive banner with a skull and crossbones in it. They look hostile.
Your players are playing real, living characters. The obvious should always be shared; after all, they have eyes, ears, noses, etc. Whatever they can pick up with their senses should be made known to them.
However, other than a picture and maybe some mechanical terms like race and class you should not show any stats about these things. After all; these things aren't clearly visible. Just because you meet someone in the street doesn't mean you suddenly know anything about their fighting style.
Anything your characters would know, even if your players don't
Is one of players a Ranger trained in the art of tracking and hunting Orcs? Then the character probably knows a lot more about Orcs than the player does. In this case, you can share information that the character would reasonably have picked up, even though there's no immediate sign of it.
"Orc shamans favor spells that summon fire and increase the size and strength of their followers", for example, can be shared with a character who is familiar with the fighting style of such creatures.
You can, or can not, depending on your personal style, either describe these abilities in mechanical terms (that is; showing part of the npc stats to the player(s) involved, or reading from them) or just describe these things in more thematic terms. It depends mostly on the kind of game you play and where your focus is.
Anything your players researched ingame
If your players take time to ask around about the Black Guild of Thieves, then they suddenly bump into members of it, you can share more details that your characters learned in their research. For example; "The guy to the left has the special kind of curved dagger use to paralyse its target."
Here, again, based on your personal style you can either describe the effects of this gruesome poison, or simply explain the mechanics. Your characters would have very indepth knowledge of this poison and these characters based on research, so they can have a lot of information.
Sharing an entire sheet
The only reason I could see you sharing an entire character sheet with the players is if the players do extensive research towards a very specific creature. Once you hit the point where the players, before meeting a person, know everything about him, sharing the sheet might be by far the easiest way to convey all the information they would learn.
But I think this would require a special kind of occassion and enemy. Normally speaking, don't share too much. It might even ruin the fun, because knowing everything that might happen can quickly become boring.
Sharing health amounts and mechanical effects
As for sharing things like health amounts and other ingame statistics; that's usually up to personal preference. Sharing it freely allows players more control over what they do, but will also turn the experience into more of a game, while keeping all the information hidden will turn the game more into a story but will also make it harder for the players to win.
That part, I think, is really up to the GM and their own group to decide. It also depends somewhat on the kind of game being played by the way; some are more focused on mechanics than others. But I cannot really help you there as I do not know anything of the Dragon Age RPG.
In general, no.
In a game with a realistic tone players shouldn't have access to the hard statistics of NPCs. I'm not familiar with the Dragon Age pen-and-paper game, but from what I know of the video game the tone is realistic with leanings toward human drama.
What I'm getting at is that it's not very realistic for a character to have specific and accurate information about another person/creature. It makes more sense for characters to have more general information from what they can notice (see, smell, hear) about an NPC, such as if they are stronger or better armored than normal, or from what they already know about them (previous knowledge, skills, experience).
Think about it like this, if you were walking down the street you would easily be able to tell some things about the people you passed just by looking like if they are rich or poor, healthy or sickly, etc., but it would be harder to tell what kinds of jobs they have, if they are good at fighting, playing the guitar, or lock picking, but it's not possible to know that that woman over there has a Strength of 18 and a skill of 13 in Bomb Disposal.
In terms of gameplay it translates as such: give your players descriptions of NPCs that highlight obvious features ("the werewolf has huge, chiseled muscles"), let them use their skills to uncover less obvious facts that they may notice or know from experience ("you remember that werewolves are afraid of fire"), but never just straight-up show them the character sheet.
This really depends on the type of game you are trying to run. Most GM's that I've interacted with (myself included) don't give exact numbers on stats for NPC's. Many only give descriptions that can help to glean close to the stats of the NPC in the scenario.
Health is a bit of a grey area compared to the rest. Some GM's give a complete tally, some only give descriptions of damage taken (my choice), some don't say anything until the NPC is mortally wounded.
The more numbers you give your players, the less like a "role-playing" game it feels like to many, and the more like a "roll-playing" game it feels like instead. Find what you want your game to feel like, and work from there.
How you decide to play is up to you, however here is my opinion.
It makes sense to describe any physical (or verbal) attributes that may "hint" at what their abilities are, however directly showing any numeric value loses the player immersion.
If you wanted to pick-pocket a NPC you shouldn't know what's in the NPC's pocket. However, by looking at the NPC you may suspect different things based on the appearance of a beggar (rags) or nobleman (colorful silk). Skills can be deduced the same way based on how the NPC presents itself (accent, good posture, carrying a staff).
Complete stat block - no.
Unless characters have studied/know the enemies to certain degree. For example if players go to exterminate some spiders that live in caves under university and said university studied these monsters for considerable amount of time, they would most likely have some information about said spiders and players could go and read them - effectively acquiring the knowledge presented in the stat block. Or something very close to it.
Of course, once players kill the first spider, they will be able to remember how many hitpoints it had, which rolls failed etc. - effectively creating statblock of their own. (This could be interesting campaign quest - to go acquire knowledge about monsters in some area and return with something as accurate as possible.)
Also bear in mind that monsters usually make sense when it comes what players can expect from them. If a spider suddenly starts breathing fire - that is something really wierd and as a PC I would be confused and question the logic behind it. However when said spider bites me and I start feeling bad, well I guess I better get something against the poison that is trying to kill me right now.
Regarding hitpoints total/remaining - maybe
In D&D 4e, when you reduce enemy under half of his hitpoints, he becomes bloodied which is status that players will know since it interacts with many abilities. This way players can count how many HP said creature has remaining. But generally speaking I prefer describing the health status of enemies in more than just three states (okey/bloodied/dead) -> describing health status of the enemy as it could be observed externally is something to consider as well. (The guard looks barely injured/ is miraculously still standing despite all the serious wounds he has suffered)