Well, there's a lot to the answers for all those questions. I have most of the parts so far and have started a build thread to detail each of these upgrades -
http://www.fordraptorforum.com/f260/other-800a-owners-my-800a-build-thread-58519/ But, I think I can clarify some things easily.
For the Sync 3 8" upgrade, you can use the base unit amp. The 801As do the same. You can program it with FORScan. 4Dtech and OEMRadioSolutions charge that much for their kit because they did the hard part - making the harness, programming the APIM, and sourcing all the parts. If you source all the parts yourself, have some minor electrical DIY skills, and can do some basic changes in FORScan (super, super easy - "programming" is a much scarier word that what it actually involves), you can do it for much cheaper. Props to them for making a plug and play product, but I don't mind spending a couple hours to save a thousand or more. Many XL and XLT owners have done this upgrade on the F-150 forum without any issue with amps. Once I do mine, I'll post a full write-up.
Heated seats for $140 using the 2014 heating elements. They are the same as the 15+ but can be bought separately. The bezel I got for the 8" sync upgrades has the heated seat buttons populated. Again, a little DIY wiring and you're GTG.
These leather seats are going to be a piece of cake vs. the 69 Bronco seats I re-upholstered. Not much ring work since these are zippered covers.
There is an awesome member on another forum that sells the instrument clusters with the mileage and engine hours to match yours, pre-programmed to your VIN and plug and play. Many other non-raptor F-150s have done this upgrade. Pricing varies on what he can get the clusters at, so YMMV. I just wanted to post so others have a ballpark on how much this would run them.
I'm actually a fan of the windowless rear window. I've had a truck before and never really used it. I actually really like the rear window visibility without the vertical bars from the rear sliding window. If a passenger needs to access the bed while the truck is in motion, that's what the side steps are for, right?
BTW - love the lead foot. Such an awesome color. I couldn't find one and black matched my wife's car, so I went black to make her smile.