Hey glad to see people still playing this I just started about a month ago and just got sucked in it, let me try to give you some tips I learned.
For your mages I wouldn't split them too thin like that meaning you shouldn't give them stats in strength and int at the same time because they won't excel later on in the game. Never really put any melee weapons on the mages because they seem too squishy and usually don't get touched much and stay back with spells.your Mage will rape if you just bump his int because you will need less AP for your spells the more int you have, meaning if you don't put much int because you put some in strength your spells will need lots of points to be cast instead of a measly cost later on when your stats are high. I don't put any in perception and just keep speed and constitution the same level like and bump my int to like 15 by kid game so just get around 10 just do be able to use lots of ap for spells and bump the rest in constitution and speed equally.rule of thumb I heard on these boards is to never have more ap in the beginning of the fight than the max you can have meaning don't make your speed get so high that you start with more ap than you actually have because you will get penalized for it .
As for madora and witchcraft ye go for it I have it on my melee characters and they constantly use buffs and stuff like charm when an enemy gets too close to you so you can easily save yourself. You don't need to bump any in into a melee strength character at all , I find just being able to use the basic spells on witchcraft on my rogue is enough to keep him alive as I want him to rape in melee not magic so I don't spread too much points like that everywhere . So don't be getting that intelligence to high levels on non magic.
For your last question defently go with the bow because of all the elemental arrows you get in the beginning they will save the day for a lot of upcoming fights, they certainly did for me , but then again I'm not sure if you can use them with a crossbow gotta try it out so can't really say. Hopefully I gave you something you can use , great game once you get the gist of it , I thought I was gonna sell it the first week I got it but na this one staying with me.