Best unarmed fighter/martial artist + other questions.

[Alpha Stryke]

Should I go fighter or rogue, and why?

What other skill should I master, apart from unarmed?

What is the main stat for a martial artist, STR or DEX? Should I pump any other stat?

I have heard it is only possible to fully master 2 skills per PC. Is that true? If true, can I have points in other skills as well or should all points go into these two skills?

What is the highest possible level a party of 4 can reach by end game?

I plan on having 2 fighters and 2 mages. Anything wrong with this?

What is the main stat for a mage? Willpower? Should I raise anything else?

What is the max a stat can be raised to?

How many traits does a PC get, and at which levels does he get them?

[Komag]

A couple thoughts:
You can only usually get enough skill points to master (50) in one skill at the expense of nearly everything else.
Theoretically the maximum level you can reach is infinite, as there are some re-spawning areas, but practically speaking you may hit 13-15 by the end.

[Merethif]

Should I go fighter or rogue, and why?

A matter of preference really. I've finished game with two unarmed rogues and one unarmed fighter (each in different party of course) and there's no big difference.

What other skill should I master, apart from unarmed?

If you're going to master Unarmed put all points in unarmed. You will get some lefovers just before final battle so it really doesn't matter where you put those points. 2 points in Dodge in a good solution for a front row unarmed rogue. Unarmed fighter may chose 2 Armour or 2 Athletic.
You can also ignore mastering Unarmed and mix it with other skill. I had a rogue with 30 Unarmed/24 Dodge and she got awesome Evasion but less power then pure unarmed rogue. I think you can mix Unarmed with Armour in case of fighter too. Like 16 points in Armour (to equip heavy gear) and rest in Unarmed.

What is the main stat for a martial artist, STR or DEX? Should I pump any other stat?

Vitality, if he's going to fight from a first row. STR increase damage and DEX increase both: Accuracy and Evasion, so I always put more points in Dex.

I have heard it is only possible to fully master 2 skills per PC. Is that true? If true, can I have points in other skills as well or should all points go into these two skills?

Actually it's one skill only as Komag mentioned. Anyway putting points in more skills then one or two is probably a waste (unless we're talking about mages).

I plan on having 2 fighters and 2 mages. Anything wrong with this?

Everything fine. Personally I haven't played with such party but all combinations are viable. I've finished the game with two parties of 3 rogues and a mage (different builds, with mage in front row during second playthrough), party of four mages and random generated party with two fighters, minotaur mage and insectoid rogue.
Just remember you have limited equipment so four rogues with daggers won't work, but four rouges (dagger/unarmed/bow/throwing axes) is a way to go.
Also fighters in second row are mostly useless, so even though 4 mages or 4 rogues make a perfect party, party of 4 fighters isn't advised.

What is the main stat for a mage? Willpower? Should I raise anything else?

Because you can't put all starting points in one stat, rest should be put in Vitality. Unless it's so called mage-tank, who will cast spells from first row, where you can consider more points in Vitality then Willpower.

What is the max a stat can be raised to?

I think there's no limit. At first level you can pu max 6 points to a single stat though. Note that stats increase only with bonuses from skills.

How many traits does a PC get, and at which levels does he get them?

2 traits on level 1 only. Other bonuses comes with skills.