#3, don't use steel! If you go this route, use a brass nipple otherwise down the line, you'll be cursing when the water starts to show up and make rust stains on things. Soldering isn't really all that bad. For probably $10 in extra fittings and some sections of pipe, you can practice a bit to get the feel of it. You can use compression fittings on pex, but you need to either pick one up in a package for pex, or pick up the SS ferrules that reinforce the pipe so you can compress the ring. It's pretty hard to over tighten a compression fitting...it certainly can be done, but it isn't catastrophic, it just means that you can't reuse that bit of pipe since you will put a crimp in it. All of the valves also come with a crimp barb for pex on them if you decide to go that route. If a compression fitting is tight enough, you won't be able to turn it or pull it off. If it's too loose, it will leak. There's room in between. There is also a system to crimp copper, but the tool is fairly expensive. You use special fittings.
The gray end of the Sharbite if for PB