Even 1 sub in the PROPER enclosure will sound better and get louder than a buncha mix and match subs and enclosures... and you'll be surprised what little power you'll need to do it if the enclosure is CORRECT
Even a 350 watt sub can sound ok for what it is... having the enclosure designed and built is one of the most important aspects of setting up a car audio system... I'd decide what you're gonna run 1st, then worry about the amp second. 1 sub or two and what fits and what configuration will work best for your vehicle... it can sound good either way, but proper enclosure design is super important and even 400 watts on a single 12 can get it done if boxed correctly.