I would put the spa return check valve lower down, after the merge from the pool/spa three way. This isn't crucial, but it does help prevent some possible secondary problems.
You don't usually need a check valve between the heater and the SWG, unless they are forced to be fairly close together.
I can't think of any reason to put a check valve on the blower pipe (I assume that is a check valve).
It is often nice to have a three way that selects between skimmers and main drain, hardly essential, but nice.
You may want to orient a few of the three way valves differently. By default the middle port (the one with no port opposite it) can't be turned off. That makes the cleaner 3-way problematic. The stops can be adjusted to solve this issue, but it is more obvious to users, especially future users, to plumb them the other (standard) way.