So I'm currently using some pvc pipe for my inlet and its about 7.5ft and my outlet is about 3 feet. I'm wondering will this affect how fast I can get the water in the filter. Also affect my water flow/ current?
Flex PVC or rigid plumbing pipe? Sump or canister?
You'll have more resistance on the longer side, but otherwise I'd not worry too much about it. Rules of thumb include shorter's better, as is smoother corners (not 90 elbows) and bigger pipes if/when you can, particularly on longer stretches.
If it's a permanent install (IE you won't need to adjust any time soon) then cut the 7 down to 3, or as short as you can. Otherwise don't worry too much, just try to keep the lines straight/simple & corners smooth.
Technically in a closed loop like a canister. The inlet and outlet should be the same length. This is because the gravity of the input helps push the output and takes the head pressure off of the return pump, essentially making for zero head height. This maximizes the gph you will see out of the pump. With that all said if one hose is longer then the other, I doubt you will see too much noticeable loss in performance from your canister.