Welcome to the site Noel!
That's a lot of questions
- I'd recommend the Lenz System or Ecos
- 5A should be plenty
- Most systems will now run from iphone and ipad apps, might not be rotary, but gives you a lot of flexibility and 'wifi' control (so no line of sight worries like with some of the older IR based systems)
Some of the older models may not be DCC compatible, or may be too much work to get there, it all depends on how you want to run the layout, and the range of stock. Depending on the layout structure, you could even have some loops or lines run DC, while others run DCC