I am guessing that if I don't buy the Float Fuel Sending Units or Landing Lights that I will have to find them from another company. Aren't those two things kind of a necessity? .
You can get them from many different companies. Like most things in life, pricing and quality varies. I would recommend getting the fuel senders and the Duckworks 55w HIDs from Vans. You can get other products a little less expensive, but might as well throw them in the wing kit to save a little on shipping. Also get the 3/4 flexible conduit from Vans. Get the 50' roll. What you don't use on the wings, you'll use in the fuselage.
The electric aileron trim sounds pretty cool. I think I would enjoy having it. Also, I would like to have auto pilot. Is the TruTrak roll servo what I need? Where do I buy it from? I would also like my plane to be set up for IFR. Is their anything else I need to install in the wing for that purpose?.
Electrim trim is almost a must have on a RV-10. You get it from Vans. You can get the Trutrak roll servo for the RV-10 from SteinAir, Aerotronics, Stark, aircraftextras.com and many other places. These you can delay the purchase if needed to stretch finances. Unless you're building fulltime or have a quickbuild, it will be awhile bfore you need them. They'll be one of the last items you'll install in the wing. Just be sure to make apprpriate holes in you conduit before putting the bottom skins on. You may also want to consider getting a harness from SteinAir for the servo too.
For IFR, you'll also need a heated pitot. You really only have two choices. Gretz from Angus Aviation or Dynon. SteinAir sells both or you can get directly from both vendors. Gretz has a controller board that automatically controls turning on and off the heat. The Dynon has an AOA function that works with a Dynon EFIS. I went with the Gretz. Like Bob mentioned above, you'll need the pitot mount to cut a hole in the bottom skin, as well as add a double that isn't in the plans. Both of these pitots use the Gretz mount.
As far as the lighting goes, I am ok with basic stuff. I do not want to spend money on things that are not necessary. However, I do like electric trim and would like autopilot and having the plane capable for IFR.
IFR means different things to different people. Paul Dye wrote an excellent article in opne of the RVators last year about selecting the appropriate hardware for you mission and how to appropriately mitigate risk with backup equipment. I don't have the exact reference handy, but I can look it up. You can download past issues from Vans.
Last but not least, read Tim Olson's web site (myrv10.com). You'll find plenty of the options that are mentioned here. Also, the "gotachas" pages are priceless. If you don't read them, you're bound to repeat them first hand.
bob