I really don't see how Kreider to Toronto would work. I assume the Leafs would need to dump a salary and there's no way I can see the Rangers taking Zaitsev back without a monster sweetener. Like a really good prospect a la the Teravainen/Bickell situation. Then you need to give up what McKenzie referred to as a "building block player" on top of that? Seems like the Leafs would balk at that price.
You're on the right path.
For this season, TOR can add a lot of cap, even when you factor in the 9M Leafs want to leave on the table for Horton not to be on LTIR, and to have no bonus overage. They are still left with the equivalent of 8M today, and 11M come actual deadline day, to spend on additions.
The actual issue is next season, however, that is the off-seasons issue, quite frankly.
I think no matter the return, Brown goes back, simply because hes a young roster player who can be in the Rangers top 9, especially if Krieder, maybe Zucc, maybe Hayes, get dealt. I think if it was a McQuaid + Krieder type thing, Hainsey, not Zaitsev, would be the one dealt to off-set some of the cap space, simply because he expires at the end of the year, and can simply slide into McQuaid's spot on the Rangers. However that's simply my speculation.
If it's JUST Kreider, I think you're looking at the standard, Roster Player, Prospect, Draft Pick. If it's Krieder + McQuaid, I see it as Roster Forward, Roster D-man, Prospect, Draft Pick, Lesser Prospect/Draft Pick