Well being new to the hobby, use track power first off as having the USA GP-38 set up for battery power would be a little much for a new guy....and if you paid to have it done may cost you a pretty penny!/DesktopModules/NTForums/themes/mls/emoticons/crazy.gif
First and formost you have to decide just what you want to do with your RR, and decide how much you CAN spend to do so...that will govern the most bang for your buck!
My suggestion is to find a club in your area and start picking brains!
Maybe there you will see various brands of R/C units, so you can decide what works best for you after watching, and or quite possibly auditioning theirs when it comes time to switch to R/C....remember that Aristo engines come already set up for battery power...USA does not!
As far as power supplies My suggestion is to start with at least a 5 amp power supply, 8-10 would be plenty for room to grow...check out Aristo, Bridgewerks, not sure of what other brands out there.
Track....do not use Bachman for outside it will rust! I use Aristo and AMS flex..USA has very good track also. LGB good luck finding that one.
If you are going to do track power outside, I suggest stainless steele track, and Hillman rail clamps...if you intend to switch to R/C and battery power..then the SS track will be a useless expense down the road, and the money you save by not buying the SS track and clamps will pay for a control of your choice.
The interum track cleaning of the brass track untill you get into R/C won't be that bad.
So in closing, again you have to decide just how much you can spend, but 1st and formost you really need to decide just what you want to do with your RR....join a club...pick brains...volenteer for work sessions to learn how to do what we do so you don't have to pay for it to be done, thus being able to spend MORE on your trains!!
Since we started our club of River City Rail Roaders there are 6-7 members that have built RRs for the 1st time or EXPANDED their existing lines....and have had 2-3 members come over to the dark side of battery power.
I myself have learned so much valiable knolledge from this experience, and can state I am only scratching the surface.
Hope this helps
Bubba