no worries for noob questions man, its always a learning curve, even for the pros. Anyone who feigns 100% knowledge is a liar
1) i have the same quandary for the older childs car and am going to get an american bass xd 12" for around $90, you could get 2 of them for 180 and be better off than the audio pipe stuff. Skar makes good stuff for the price too, but the guy who owns the company is a d-bag and it seems that the community frowns upon supporting him.
2) yes, a new amp would do you well. if youre running 2 12"s, get dual 4 ohm woofers and wire them to 2 ohms each, then down to 1 at the amp. I just got a SoundQubed S1-1250 and that would do very well for you and its $150. Plus your electrical in the trunk at least looks strong
that box will definitely do well if youre not wanting to build one