I use custom strings on my bass (6 string tuned E A D G B E like a guitar). Your fingers will toughen up after a while, but you have to suck it up until then. If you are a "hard" player like I am, meaning you play aggressively, I would use at least a 100 for your E string...it's just about trial and error and finding what works best for you.
As far as playing the fast stuff, it's all about what your technique is. I use my fingers for most of the motion, and get a little wrist action in there when needed. My arm stays pretty still. To practice, I would suggest just playing some galloping riffs (a la Steve Harris of Iron Maiden) on one open string at a time, and practice going from string to string - that may not be the type of music you play, but it will get your timing and endurance up to speed in a big way (and use 2 fingers - it's harder but you will be moire accurate). I would also do the same thing with triplets (a la the intro to Disposable Heroes) and some even faster stuff like the rhythm to Whiplash...I used to sit there for hours, sometimes not even plugged in, practicing those rhythms, and it madew a huge difference in my playing.
The only other suggestion I have is to find your own style and what works for the way you feel most comfortable. Make sure your basic fundamentals are there, but make your playing technique your own.
Lastly, check different strap lengths to find the most comfortable for you...playing with your bass slung WAY low looks cool - but it makes it really hard to play aggressively. I keep mine pretty high, and while it may not look as ruthless as some other guys, I can thrash out some fast rhythms and solos...
That's my 2 cents...
