1) Most 6" housings will work - Cree has an LR6 compatibility listing on their website, but I can't find one for the CR6 or CR4. I haven't run into one that didn't work, occasionally with minor and easy modification like bending a wire or removing an piece intended to hold a separate trim bezel in place, but many as is.

2) the CR4 won't look weird at all next to an CR6-800L, because the smaller surface area of the CR4 makes it look much brighter than the 575L version of the CR6 when you look up at it, despite giving off the same amount of light. I haven't seen a 800L CR6 yet, but I'm guessing it will match in appearance with the CR4 better than the 575L version does.

3) Don't know here, but a halogen MR16 tends to be about 2900K which matches the 2700K CR4/CR6 well. For LED MR16s, look for a 2700K model with the best possible color rendering (CRI). Prefer gimbals to eyeballs for aesthetic reasons, and traditional wall washers eat up some of the light given off by the omnidirectional light bulb.

I'm confused about what type of housing to buy that will fit Cree-CR4s. Home Depot sells a Halo 4" CFL Insulation Contact Air-Tite Remodel Housing. Will that work?

No. The base has to be either a E26 medium base or GU24.

davidtay, who makes a 4" IC Remodel housing that will work with Cree-CR4-E26? I'm having trouble finding one.

Possible candidate for consideration
Halo 4" LED Retrofit Housing - H995RICAT

Thank you, I'm going to give this a try.

The Halo H995RICAT isn't going to work. It uses Halo's own LED connector and not the standard E26 socket.

If you need to use a IC-rated remodel can, you probably need to switch to the GU24 version of the Cree CR4 and use the Liton LH99RICA-LLF-GU24.

The Liton remodel can is the first one I've seen with a loose GU24 socket which works well with the Cree CR4. Some of the other remodel cans have a fixed GU24 socket and the leads on the CR4 aren't quite long enough.