1. Trials = low gear, no seats, strong brakes ; bmx = ridiculously high gear, has a seat, pretty poor(or no ) brakes 2. Fairly practical i guess, i ride mine to college most days...mines extremely low geared with virtually no speed, but loads of acceleration, a real hill climbing gear 3. You can pick up a nice specced beginners bike for as little as £250 nowadays....e.g http://www.tartybikes.co.uk/product.php?id=2115 second hand they're even cheaper 4. For a beginner it depends where you've started...if you're small and quite young or rode a bmx ...then mod, if you've ridden a mountain bike, then stock....if you ride street or dirt jump then probably a 24" 5. A lot of the videos you were probably looking at were either oldskool videos, or street trials ( bunny hops, spins kinda stuff ) Modern trials bikes look more like this nowadays: