sell the xover and save up for new HU, just use the  hi pass and lo pass filters on the amp

can use stock HU with the alpine 4ch first because it can accept speaker level input, no need to buy hi-lo convertor

just power just the comps first and later the sub.

in car audio, waht u pay is what u get, thats why component set always more expensive than coaxials, and of coz sounds a lot better too.

instead of using amp + coaxials, better use that money just buy component set.  add amp when u have budget later on...