i did nearly the same, deck, splits, amp and sub myself.

its actually quite simple, about the hardest thing to do would be the amp but all you need is a little thought and a test light. if you already have a deck in place its even easier as you just use the same wiring points, ( cut the old deck plug off and use test light to figure out which wire does what ).

give it a go, if not theres a few people on here that have done it themselves and could probably help, i would but i have to work this weekend!