1. to the best of my knowledge, no one has done a complete tree, in a single-page 'tree' format...but you can find a whole lot of helpful/useful/interesting information at desdemona's site
here . look specifically at the 'skills' button toward the top.
2. you're
almost there. yes, first you must 'purchase' the
ability to learn the skill
to a particular level , in your case level 6 (though there are some 'free' books to be found), next you must apply a skillpoint for each level of mastery you wish to gain.
example: bought level 6 repair, now must devote 6 skillpoints to attain 6th level of mastery - though a lesser amount of points will work also, just not as well.
3. everyone is going to have a differing view on this - and all are valid.
i personally like to have one melee and one ranged attack character. i think they provide the best compliment.
now wether you choose that ranged attack to be magic use or bow use is a personal decision.
if you were going to make one of your characters a magic user now, you
may wish to start over, but that
probably isn't necessary.
skillpoints devoted to a specific skill are 'sellable' so you can recoup most - it's the distributed attribute points you need to consider. obviously a mace wielder is going to focus on strength while a magic user is going to be focused on intelligence.
so this will somewhat depend on how far you've gone into the game (what level you've attained). it seems that most people finish the game around 31-32 level, so that should give you an idea of where you presently are.
my guess would be that as long as you're focused from here on out, you'll be fine with the switch.
good luck.
