Today setting up a Pro Channel template.
Looking for suggestions on the best type of compressor / settings when Guitar has alot of palm mutes.
I think fast attack slow release, not sure which milliseconds to use.

The type and settings for the compressor depend on what you want to do, the speed of the playing, how different the palm mutes are etc.  If you want to even out all the notes then a faster attack may help with that. If you want to accentuate the attack then do a slower one. 
 
One suggestion is to take the threshold way down so the compression is fairly obvious and play with the attach and release to see what they do Then raise the threshold until you get the effect you are after.

There are a few ways to use compressors. One way is an always on kind of approach blended with an uncompressed track. This can be ok if you are wanting to reduce the dynamic range. Usually this gets a low threshold and long release. This tends to increase noise some.

The other way is to basically quickly bring up the volume of a sound like a snare hit right after the hit them let it fade down fast to avoid noise. This helps slightly lengthen the hit and give the feeling that it is louder than it is without increasing noise the rest of the time.

Most guitar players fall closer to the always on than snare type setting.

There are lots of other ways to use compressors. This is a huge generalization, but it might help you.

Thanks for good starting points!