Just a thought, but you might want to also consider a Lionel ZW-L transformer. It's similar to having 4 powerhouse 180s and 4 powermasters, but all in one unit. Lots of flexibility for both conventional and command control, powering accessories, etc. Might be nice if you plan to expand from your original plan above (thinking of the 2006 25x15 layout you mentioned).
I can't begin to describe all it's features so the manual is attached below.
