SoloJJ
Hello and Welcome to the Forum!

Your trains and track should work well with the CW-80.
As long as your 3 rail track isn't rusted to the disintegration point, use it!
Some of my track is  from the 1920's & 30's. rusty/discolored - NATURAL WEATHERING. works just as well as the newer track that I have.  As lng as the pins connect tightly and it's clean, 3 rail is good.
I do have some fastrack type track and I personally don't like the noise it makes.
You can't leave that little space between the track sections as with 3 rail that gives you the clickety clack as she goes roundy round.
If your MTH will operate in conventional mode, no problem, if it will operate on the curves that you have.
Big locomotives need wide curves, not sure what curves it requires, O-54?, O-72? minimum, your instruction book shoould say.

If you still have your original transformer and it works, use it to supply power for your accessories.

Happy Rails.
Dave