Sillcock dilema

I'm relocating my sillcock so it's easier to access. I will be rerouting the pipes in my crawl space, running pex off the current copper pipe about 10-12' to another wall then through the cinder block. The copper pipe is not insulated but we haven't had any problems with freezing ever. We are in Virginia so some cold but not brutal. Is it ok to run the pex with no insulation? If I need to insulate I could either use get some foam wrapper to put around them or drill through the joists and tuck the pex into the batting there. Is one way better than the other? One more question: I see mention of putting a sleeve around the sillcock as it passes through the cinder block, using slightly larger pipe. I think to prevent corrosion(?). Is this necessary? Or just seal around with some silicon? Thanks!!

Hey all, The tenants for one of my rental units (townhouse) recently started complaining of low water pressure, only when using hot water. They notice the issue in the shower, and in the kitchen faucet. I witnessed the issue in the kitchen faucet and the pressure drop is certainly noticeable. Any advice on where to start? Replace kitchen faucet, if that doesn't work start digging further? I'm guessing that this is going to be related to hot water heater...but am lost after that. If this isn't a simple fix I guess a plumber will need to be involved. The house is 20+ years old and water heater is about 15 years old. It has copper pipes which connect to the rest of the house plumbing. Thanks in advance.