Wiring – What type of ethernet cable do I need for outdoor use

To help you with the terms, what you're looking at from above is the top plate. Frequently there are two 2x4's for a top plate. Two boards are used for added structure at the joints and extra fire proofing. This gives you about 3" of wood to drill through.

As ChrisF mentions, you should run a stud finder up and down the wall cavity near the halfway point to see if any fire blocking has been installed. This would be a single 2x4, and will almost always be in a wall if the ceilings are over 8' tall.

You'll significantly reduce the odds of insulation in the wall if you are doing this project on interior walls. You should also be avoiding any electrical in the same wall cavity (between the same two studs). You would see an outlet, switch, or wire coming out of the top plate if this were the case.

As for the actual wiring, I've used these low voltage mounting brackets for the hole in the wall. Place the bracket on the wall where you want the opening, mark the corners and sides, and cut out the drywall with a drywall saw. Test fit the bracket and file back any spots that are blocking you until you get a snug fit. Then bend the tabs back into the wall and tighten them with a pair of pliers. On that bracket, I use a modular plate (these comes with more openings if you need them) and then an ethernet jack mounted in the plate. You can also get jacks for cable, phone, stereo, etc.

Well, if you are going to split it 3-ways, buy a 3-way splitter not a 4-way. I agree with the comment from Mikes about buying a more expensive model if possible.

I would avoid a booster at all costs - power boosters add noise to the line - so yes you get a higher signal, but its noisier.

As far as minimizing signal loss, here are the top items to keep in mind:

1. Keep runs as short as possible
2. Don't splice cables together - always use a single continuous run (where possible)
3. Buy a high-quality RG6 cable. Quad Shield (usually you will see RG6-QS on the cable) provides the most shielding and helps reduce interference
4. Use high-quality compression fittings instead of crimped connectors (Thomas & Betts Snap-n-seal is my product of choice). Also make sure you install them correctly (end of internal plastic insulator flush with the inside of the fitting, ground braid properly folded back, cable stripped correctly, no nicks in wire, etc.).