The Driver door switch at operates the rear windows? Dorman makes a reproduction switch (Dorman #49235) that you can get/order from any autoparts store. I find that most of the time that I think the switch is bad that it is usually the connector to the switch that has oxidized. just removing the connector and cleaning the contact area makes it work again.
Tunes are a personal thing. Most all of them are sold based on the TS style chip reburned to the sellers tunes. I have Beans Diesel tunes and Tony Wildman tunes. Others like Gearhead, DP Tuners, and PHP tunes. That is something you will have to experience and test for yourself.
The only real drop in turbo for the OBS is Beans Diesel D66 turbo. This is a modified turbo from the factory metal. Others are selling a very similar turbo. Other then that you are looking at either a Modded H2e or a T4 mounted turbo similar to a Cummins turbo. There a lot of turbos that you could use after converting your exhaust system to a T4 mount but this is an expensive swap. Some of us would say that the turbo is not a worthy upgrade till you are at 160/100 injectors anyway. The factory turbo can take you a long way (some have use the factory turbo with 250/200 injectors).
Injectors like tunes are a personal thing. You need to first establish a personal goal for you and your truck. Then call Cary@CP_Performance, Beans Diesel, Swamps, Justin@DP Tuner, and PHP (and others in the Sponsor section of the .ORG). All are very helpful and will tell you their personal feeling toward what you want to do. Have a lot of time to talk as there is a lot of good sponsor information out there, you just need to listen and ask more questions.