How much Transformer?

I doubt a CW80 has the juice for a legacy loco and 8 lit cars (perhaps even if they're all LED). There's just not enough amperage available.  You'd be better off buying a 180 W brick and the cab 1L/990 set now. The 180 brick is basically future proof for what it sounds like you're after. 

You probably are better off buying a larger transformer/brick and Legacy set now if you can afford it, but I think the CW-80 should be fine for what you have now and maybe even a little more.

The CW-80 is a 5 amp unit. My Legacy loco's draw anywhere from about 0.8A to about 1.4A, depending on load, speed, grade, etc.  and the lighted cars, especially if LED's, shouldn't put you anywhere close to 5A. I can run 2 Legacy loco's plus a Lion Chief on 130' feet of track with 4 lighted cars and over 20 accessories at the same time and not have an issue, so you should be good to buy a used one and be able to even add some accessories as well. 

I agree with Boilermaker1. Charles Ro had the PH-180s for around $75 a few months ago. Probably less than a CW-80 and more than twice the power. Of course you would need the Legacy 990 or Cab1L/Base1L at the same time. If you plan on a big layout with Legacy engines I would bite the bullet and get the 990 system. This is sort of the way I started out, only I started with DCS instead of Legacy.

That is kind of what I thought.  I'll save some pennies and admire my motionless locomotive in the mean time.  Thanks!