Just picked up a new amp... need sub and box suggestions

So in my quest to replace my garbage Wal-Mart Jensen amp that has finally shit the bed, i scored an Alpine M1000 at Best Buy for $200. I couldnt really pass up a $400 amp at half price, even if it kind of is overkill for what i've got. For now, i've just got a little pioneer 10 in a shitty truck box, but it was free so i'm not complaining. I ultimately want to replace the box and sub(s), but it's been so long since i've played with that shit, i don't know where to start. I like the Atrend boxes at best buy online, but i'm confused about 10s versus 12s. I was reading somewhere on here that 10s are better in downfiring applications since the 12s can hit the floor and cause damage. is this true? I'm not doing competitions or anything like that, i just like my music loud and to sound good. I listen to mainly rock/metal and the occasional jigga music, if that makes much difference in sub/box choice. Suggestions?