What he said ^
Most amps make more power at 2ohm loads so you want to wire up your solution to extract maximum power from the amp, that won't leave anything on the table. As far as power handling of subs go, that's tricky. In a lot of ways you might want to overpower the subs, which does not mean you would actually pour more power than they can handle but rather means you have ample power and headroom for good peaks and dynamics. You would't want to underpower the subs and have the amp cranked on max, that's a lot worse than overpowering. Usually when amps start hitting limits is where they distort, heat up, compress, and all that. A little extra power is good. But again, you would't not want way more power than the subs could handle or "wasted" power either.
You can't always go by the MFG rated power handling either. I find when you model your design in WINISD that can give you a good idea what kind of power you want or should use. Keep in mind some amps use a "peak" power while others use RMS, or more constant. Not all ratings on amps are the same either. I think what you are trying to do has been done one hundred times before so you should be fine. Stick with one of the proven set ups and it should work great.
Do you need help with custom box still ?
"Too much is almost enough. Anything in life worth doing is worth overdoing. Moderation is for cowards."