Also, if i try to setup Mesh and it does not work the warning says it can't be shut off unless I default the main unit and re-set up.
Let's say it doesn't work, too far etc. - would there be a problem leaving Mesh on and still setting up the Guest house with an unleashed AP with a PTP connection directly? In other words will the Mesh and direct link back over PTP mess with each other - create a loop etc.?
Yes, setting up Mesh is very easy - just a click away. If you are going to setup a mesh using other Unleashed APs (which seems like a possibility based on your brief description about the environment) you first test Mesh connectivity before mounting it on a ceiling or other inaccessible places to avoid Mesh AP staying a limbo state.