I have a four door as well. Good luck with your build, right now I assume you have the shitty ass d16y7. The automatic swap isn't too hard, it is just time consuming more than anything else.

If you are looking for cheap power/increase. I honestly would say go with what I have in my car now. I have a Automatic LS motor with a B16 transmission/b16 flywheel only with intake header and exhaust. Mind you, it isn't fast at all, but it is quick for what it is. Not counting the b16 I put in, I probably have about 1000 wrapped up into this swap, thats:

-Hasport mounts
-Hasport linkages with poly eurathane bushings and skunk2 weighted knob and shifter
-B16 trans with clutch/flywheel
-B18b1 engine.

If you ever need any help once you get converted over to 5 speed or whatever and you need some help. Let me know and I will help out where ever I can.