Go to the school and read the real copy of the real POH for the aircraft you are going to fly.
Or, possibly better, don't bother. Your instructor will teach you this stuff, and will be a lot less irritated if he doesn't first have to un-teach you some wrong numbers you've picked up from elsewhere!
Re W&B: it's easy to overload a 152 - just put two not-all-that-heavy-honest-guv grown up men in it and fill the tanks. It's not easy to get it out of balance, (once you work out that if you've got two heavy pilots they're probably also tall so you probably don't have the seats in their most forward position).
As Malcolm says, no change you'll notice with fuel burn.
Whether it's good or bad as a trainer, well now, you risk getting into religious war territory here ...