Achtung, I shall prodice a tl;dr.
Regarding that starting mercs question - depends on who is available at the moment. And, of course depends on difficulty and starting money.
Also, it's okay just to pick up guys whose voiceset you like. Steroid and Barry anno the fuck out of me, so the above combination desn't work for me.
For starting team you need: a medic, a militia trainer, and 2-3 good soldiers. A repairman might be useful, if you have bobby ray's stock set to something else than default, so that you can buy some worthwile used stuff once you hit Drassen.
Ira is available almost from the very start (but she is an annoying type), and can be used as an ok medic and trainer (she has teaching speciality ang get a training bonus as a member of the rebels - her leadership is low in the beginning, but trains very fast.)
When MERC opens up on day 3, you can hire Gasket for all your repair needs (desn't like Russians though), and who also happens to be the only guy out of the bunch worth the money.
You don't have to take Ira nor Gasket, just be mindful that they're available.
As for the guys who'll do actual shooting, you want good health, agility and marksmanship (Good, meaning 80 and above. 70-something is fine, too).
Above average dexterity helps a bit as well.
Personally, I choose out of the following: Buzz (96 MRK, reasonably priced), Len (good trainer), Wolf (can repair stuff), Igor, Stephen
I also like to give Fox a chance - makes a decent medic and is ambidextrous. MRK seems pitifuly low, but actually can be trained quite fast up to 75+, just give her two pistols and use in close quarters.
You don't need lockpics to get past locks. A crowbar will suffice - you need to alternate between kicking the lock and prying it (so that you don't get the annoying Never gonna happen comment from the merc). It's also a great way of training strength.
Later in the game you'll want a demolitions guy (meaning 50 EXP and above), there are a few available quite cheap. BUT, it's really easy to train EXP by setting and recovering mines, so consider training one up yourself. If you have the patience.
You'll also want someone who can handle a heavy weapon. But that usually comes much later.
You can take zero for repair and explosives
That's what most people do, but not necessarily the only nor the best way. You actually lose some points when you set the skill to 0.
IMP creation actually deserves it's own bit:
Remember that in 1.13 you can have more than one IMP merc, so long as you use a different voice and photo for each.
You can also tweak some of the values used in character creation in the .ini file.
You can use this to cheat very easy, but I'll just leave this to your own conscience. Personally, I just like to set the max value for skills to 90 and min to 25. Also, note that you can set the personality for your merc there (some of the settings do nothing though)
The stats:
Remember, that if you set a stat to a low value, it'll be easy to train that in the beginning. It's useful to consider this, if you don't need to have above 60 in something from the very start.
Maxed wisdom is a must. It'll make all the other stats go up faster.
Health - don't be stingy here. It's both useful and hard to train. 70+ recommended. I put as many as I can here.
Agility - you want around 80 here for your IMP (and all mercs), as it affects action points.
Dexterity - I like to have 70, but 60 is fine, too. It helps a tiny bit when aiming, but generally has some effect on Medical and Repair. It's also used in hand to hand combat.
Strength - Can be trained easily. However, if it's too low, you'll get tired more often. If I'm looking for spare points, I usually take a few off here.
Marksmanship - appears to be the most important of the skills, but actually don't fall into the trap of maxing it. Since you'll be shooting all the time most likely, it'll train quite fast on it's own. I go for between 70-80. 85 feels a bit like a waste.
Leadership , Explosives, Medic, Repair - now, the values here depend on what type of guy do you want. It is often advised that you should set all these as low as possible (even to 0), and focus on building a mean fighting machine. It's acceptable, but you'll miss out a few opportunities to make your merc useful (but can be a viable option if you set the option that 0 value skills are trainable).
On the other hand, don't fall into a trap of trying to make your merc useful at everything. Usually, you wont have time to train people, repair AND play doctor, so just pick two and focus on these.
A more conservative approach is to give your merc some Medical skill to use 1st aid. Or give him or her around 50 to make him useful as a full time doctor.
However, as long as you don't stupidly charge headlong and keep two medics in each squad, you might skip this entirely (I do).
Explosives is really easily trained to ridiculously high levels using mines. Also, setting and disraming TNT with radio detonator trains WIS, but requires EXP 80+ to pull off with a reasonable chance of success.
Repair - I actually favor this one instead of Medicine, as it seems to train up Dexterity a bit faster. Also, I am a fan of buying cheap at Bobby Ray's
Leadership - the most noticeable effect is when you train Militia. For best results pair it with teaching skill. Ira can do it for you. And there are a few other mercs who can do it as well, so you don't have to take it. It is also used when training other mercs and apparently in several dialogues (especially when recruiting).
