I am getting to the point of plumbing the equipment pad and I was wondering how much of a loss would there be using those combination 1.5"/2" (socket/spigot) valves on my setup?

As it stands I have 2" PVC run to the pool and to the equipment pad. I am running a Pentair Dynamo 1.5hp 2-speed above ground pool pump, which has a 1.5" NPT inlet. From the piping I will have a ball valve, then a union which will have a 2" to 1.5" NPT male adapter in it which will go directly into the pump. From the pump I have a 1.5" buttress union going to a 1.5" to 2" adapter street elbow. That goes via 2" PVC to the Sta-Rite System3 cartridge filter. From the filter it is all 2" to a check valve, then 3 way valve (one way will bypass the heater to the return, the other will go to the heater), then to the heater, from the heater to a check valve and ball valve (to totally isolate the heater positively if it is in bypass for service), then to the return piping (which will also have a ball valve).

Now the big question is how much flow is lost through the 1.5"/2" combo valves that are out there?

I know there is a flo-tech ball valve that is half union with that combo, a clear check valve that is configured that way, and the Jandy 4715 3 way valve also has this combo. Going with these items is almost a 1/2 cost savings going with these combo valves, but I don't want to kill the advantage of going with 2" piping and filter if going with these valves will compromise it that much.

I also have plumbed in extra 2" piping to the pool to give me options for water features or extra skimmers/returns, so it is not out of the question that I may upgrade to a higher-flowing pump in the future.

Last question is it acceptable to use "all purpose" PVC adhesive to connect CPVC piping to PVC piping? The heater (Jandy Lite2 250k) calls for CPVC connections at the heater with at least a 6" nipple, so I was going to use a close nipple with 90 degree CPVC elbows to allow for closer connections since my equipment pad space is at a premium with the heater on it.