please allow me the opportunity to say Thank You for your service to our Great County!
.....the first thing I'd do (and did when I made that same choice) was to read all I could here on MLS, LargeScaleCentral and the GR Mag forums. I spent a few months investigating and posting questions much like you did here. I also contacted a few men from the different forums and they very generously shared their experiences with me.
There are prob about 5 or 6 major players in the RC game right now. I decided that I wanted ease of use, low price, capacity to grow the system, and simple Bell and Whistle control for sound. After those months of surveying the landscape (if you will) I chose the EVO/RCS control from Remote Control Systems. Since then I've converted nearly 6 locos to work on the system which has performed flawlessly for me and the kids. (note: I'm just a happy customer, no sales rep or associate!).
with all that said...what do you need?
1. A Locomotive
2. Power Source-Battery (I've used NiCad and NiMh)
3. A Throttle/Receiver
5. Sound Card-if you want sound
I'd imagine you could install all components in the tender. It can be a little overwhelming to begin with, but help has always been just a phone call away (for me using NWRCS). All systems have a pretty loyal following (see my above referral), so you will find many reports on what works best, and why. Again, I'd encourage you to really study this over and make an informed choice. Go back into the archives here on MLS, look into the other forums mentioned to find all sorts of "How To's "and reviews. Also look into the Mfg websites for more information on what is avail and required. If you feel you may not be up to the task of installing your own system, there are shops countywide that can assist you!
Battery/RC has been a great choice here on the NBRR…we have be well pleased that we began our Journey in LS Trains via Battery Power!