I am a new GM and new to D&D. Currently, I am running the Lost Mines of Phandelver (LMoP) D&D 5e starter campaign. My group have just finished the Cragmaw Hideout section, but as we ran it we came across some situations that I was not sure how to handle.
Specifically, at a certain point the party encountered three goblins in a cave with a waterfall (area 7 "Twin pools cave" within Cragmaw Hideout). In the description of the area the book suggests that, when they spot the party, one of the goblins moves to next room (area 8 "Klarg's Cave") to warn his allies that there are intruders.
The party killed the two remaining goblins in area 7 and then moved into area 8. My questions have to do with the characters transition from one room to the other:
Is it reasonable that the warned enemies (who are hiding behind stalagmites and crates) attack the group immediately when the group enters the room (like taking the Ready action from the previous round with the condition "I attack any enemy appears at the entrance of the room")?
Is it better to start a new round every time the party enters to a new room/cave, even though a PC may have enough speed to cross a certain distance in the previous cave, and then enter the new one (in the same round)? If this is reasonable the PCs would have the chance (given that their initiative is greater than that of enemies) to use their Wisdom (Perception) as an action (assuming that the Dexterity (Stealth) check score of enemies is above players passive perception) and avoid being surprised.