First of all, congratulations, on making the choice to play the coolest instrument in the world
Squier Affinity basses are pretty OK, they do the job, but you're still paying for a name to a certain extent. I'd say for the same money, try some kind of Ibanez or Yamaha, they represent far better value for money. Generally speaking they feature far better components, woods and pickups than equivalent Squiers, are better built, and I find the necks on Ibanez basses far more appealing to play.
My Yamaha would cost just a little bit more than a Squier Jazz bass, but is built to a standard higher even than a mexican fender, and I truly love it
As for amps, if it's just a guitar practice amp, I really wouldn't want to risk playing bass through it, basses tend to put in too much bottom end punch for weak-magneted guitar speakers and have a habit of blowing them out. You'd have to play really, really quietly, and even then it'd still likely sound a bit shit. If you had a bigger guitar amp, you could probably get away with it though. It's very much worth investing in a little bass amp, there are hundreds made by marshall, crate, peavey, ashdown etc., my personal favourite is the Marshall MB-25 mk.II. I've had one for years and years now, even though I have a biiig amp for gigging etc, the little Marshall is still satisfying to my ears and puts in most of the work for home stuff.
Good luck with bass, anything you wanna ask, no matter how retarded it may seem, it's worth asking, better to get embarassed on a web forum than end up with a pile of useless gear