A word of advice, if I may. Don't forget to install the Arcanum Unofficial Patch, and never-never-never use RT combat option, it simply doesn't work.
Easiest is to go for one direction: magic or tech. Magic has a lot of schools but few spells, and I think limiting yourself to 3-4 school would be a good idea.
Herbology isn't very useful for magic users, since they have potions. Tech users can use it to create tech-alternative of potions.
If you play a magic user, by mid-end game you won't be able to use any of the tech transportation systems, so perhaps the transportation (or w/e it was called) magic is worth investing into. Don't invest points into Stun and/or don't use Stun if you don't want to ruin the game for yourself - the"saving throw" doesn't work, which makes the game way too easy overall.
If you play a techie, be aware that the game will likely be a bit more challenging, especially early on. If you go for rifles, beware - in early-game bullets are rare and costly. A tech character is very fun to play though, IMO better than magic-user, so it's worth the effort.
Unlike what Black Feather says, it's probably possible to dabble in both magic and tech, but you won't be good at either. It'd be fun to try it sometime, but it would definitely be a challenge.