Personally i wouldn't worry about a ball valve. To be honest if an issue came up with the condensate pump, it could easily be removed and drop a bucket underneath until you can run to a hardware store quick enough to replace it. You want as little drops and turns as possible, and if the valve will give added peace of mind, just use a pvc one. Everything looks like a solid plan! If you have 8-10" of drop, you should have plenty of room!
I dont think you would need another elbow and nipple; just drop into the condensate pump.an another elbow an nipple into pump.