specific LS swap questions

[encasedmetal]

been reading through everything I can but have some question left that hopefully some of you can answer. I am doing this on my 63' gmc btw. if you can answer only one- please chime in.
1. regarding wiring harnesses- I will be rewiring the entire truck SO is there a company that can make all of that for me or would it be best to use the LS engine harness and 1980 complete harness that I have. (I've never wired a car before but willing to give it a shot). I will be running a/c which my truck didn't originally have plus the gauges etc.
2. I won't be using my in cab gas tank and have decided to do an intank pump setup with a tank mounted under the bed. are there any originally LS powered vehicles I can fit back there or is it best to go with something like a boyd's etc?
3. when using LT designed for an LS swap in our trucks- are there any midpipes that fit as well?
4. I am really wanting to run Dakota Digital gauges with the accompanying OBD port- is there anything to know about using these or that I should consider when wiring the truck?
5. if using a t56 trans- what do I need to do to run the slave cylinder with my brake booster or do I need another type of brake booster to run that?
6. If anyone doing this swap has used a donor vehicle to do it and not just bought the engine/trans off craigslist etc- what would you recommend grabbing off of said vehicle (ie what would you not leave behind).

sorry for the long read- and thanks for the future help- hopefully it help others as well.