Villains can be built along the same lines as heroes, with a number of points based on where you want this guy to be relative to the group. If he's got as many points as one of your heroes, he'll be in a lot of trouble if he gets ganged up on unless he has some manner of ace up his sleeve. This is one reason why most of the published villains are so much more potent than PCs - they need to be able to face down a group. Practically speaking, you probably want to give a villain at least 25 points more than the highest hero in your group, and 50 might be more more reasonable. +100 is going to give you a villain suitable for hanging the campaign off of (though he still won't compare to the published villains).
For henchmen, I would make the decision based on how you intend to use them. If you really want to get into the details of one (because you like the character enough to give him a real name and a face), build him with the same number of points as a PC, but make sure to keep him attached to a brute squad whenever possible to keep him from being too much of a pushover. If you don't expect to ever see the guy again, you can be a little bit more fast and loose, and just assign him some values that are going to put him on par with the PCs.
So, that's the nice, rules respecting answer, and it will work if you're very attached to being fair, but the reality is this - between the cost of swordsman schools and sorcery and the relative ease of maxing out skills, trying to go strictly by points is an invitation for disaster. I admit, I'm a big proponent of just statting up villains and henchmen as "feels right" but that's not useful advice, so let me at least provide a few tips.
- More than anything else, you are building something relative to your players, so keep their skills and abilities in mind so you know what to challenge and what not to overshadow. For example, if one of your players has really thrown all his points into being a master swordsman with and has spiked it notably, be very careful about having a villain overshadow him there. If the villain is ALSO a master swordsman and that's his schtick, then great, but if it's not the villains strength, having him incidentally outclass the hero is just unfun.
- For a baseline, treat your party in total as a character sheet, with the highest value in each knack as the value on the villain's sheet. It is much faster to modify up and down from there than build form scratch. That guarantees the baseline can challenge the PCs appropriately, and you can then choose where he outclasses and is outclassed. For a henchman you can use the same base, but more drastically undercut the spread of stats, keeping him strong in a narrower focus.
- The actual stats (specifically the roll & Keep values) are almost trivially unimportant when it comes to villains or henchmen. Far more important are the tricks they have up their sleeve, since it's those which are going to stand out in the player's minds. Tricks might be high level swordsman skill abilities, particular sorceries or something else but those are the things that matter. As a rule of thumb, I try to give a henchman one trick and a villain at least 3.
- On the flipside, don't worry so much about the advantages and disadvantages that aren't signature tricks. Small advantages and skills can be glossed over.
- It is a horrible tragedy if your villain doesn't have an Arcana.
Anyway, it's a little ad hoc, but the system is incredibly supportive of winging it a little, so if you misjudge, it's pretty easy to course correct. Good luck!