The Warhorse J might not be such a good option, if ZW wants to use it to pull his passenger cars, as he says. While it would pull the cars, it wouldn't look good doing it. That Warhorse J came with a pretty heavy weathering job (not to mention the cranky, broken down type RailSounds Lionel put in it to simulate an old, end-of-useful life engine). It's not going to look too swift pulling some nice shiny passenger cars.
A better bet would be the 18040. Probably the most attractive traditional J Lionel ever made, with proper passenger maroon colors, unlike the Space set J, with its reddish, Postwar style trim, that doesn't match the passenger cars.
Check with Electric Railroad - they have an AC commander that can add TMCC to an engine with a Pullmor motor, which of course the J has. Put that on the 18040, and you'll have a nice engine.
Lionel also did a set of aluminum passenger cars for the 18040, with more of a satin finish that matches the engine. The MPC era J and cars you now have are painted with a relatively shiney finish. I've not seen the MPC era cars with the 18040, so can't comment on how they look together, but the finish will be different. Lionel also subsequently did another set of "traditional" N&W aluminum passenger cars, a 6 car set, these with finished interiors and passenger figures. They also have the satin type finish. If you can find those cars, that would be a great set for the 18040, I would think. All it takes is money!