Are you going to use command control? or conventional?
What is your power source to the rails? Single handle or multiple?
Do you have separate power for accessories and switches?
What types of engines are you running? Old or newer? Do you remove stuff off the rails when not running?
Three loops can have some decent amp draw if there's several engines and old lighted cars on the rails. I have to guess that you have some isolation already?
The best thing about power districts is keeping trains on separate power sources. If one derails and/or shorts somehow, the others keep running. You can actually use the same transformer if it's big enough to handle it, and just place separate fuses or breakers in line to each loop. It will also help protect modern engines from older transformers that might not have fast breakers or see it as a smaller short and just keep powering the track.
I think your question(s) in the original post could have a very wide range of responses. So "trouble" to me means keeping things running and protected.
There's a lot of good help here if you ask specific questions from here on. You already got some good advice, I just wanted to take it further.
I saw the post the other day and didn't have the time to fully answer. Sorry.
