That metal 'thing' I believe is commonly referred to as a 'mud ring' but don't quote me. It's used where you don't have the option to put a box in. It's no substitute if you're building from scratch, but if you have to drop a connection in a wall where you have limited access, it's great. They should be *very* cheap at Home Depot, Lowes, et al.
As for how to run your category 5, it's not too bad. Ensure that you do not run it parallel to any power circuits, directly over fluorescent lights, inside your ventillation shafts (unless it's plenum), or outside unless it's rated for it. If you run it outside, then back in, the wind alone, when blowing across the jacket, can cause static discharges to your equipment. I've seen cases where someone's NICs, routers, and switches were blowing ports left and right. We tried surge protectors, special ground isolation, etc.. NOTHING worked! Then, on a whim, I ran the cable INSIDE the house and it all stopped. The wind was whipping the cable around outside the house (used to avoid going through brick walls) and creating loads of static on it! (standard cat5 w/PVC jacket)
Ah, the stories that surround that jewel. What else? Make sure that your terminations are within 1/2" of the end of the twist (always). Depending on the scheme of wiring you choose, (A, B, USOC, etc.), stick with it - don't change midstream. Always leave some extra slack for error in calculations, wiring or relocation. Don't fold or make sharp bends with the cable as it effectively reduces the O.D. of the conductors allowing less current to flow. (not that it's a high current application, but the rules of physics still apply) Generally, solid conductor cable is perfect for wiring a house, but if you know there is a chance it will be moved around repeatedly or relocated often, use stranded cable.
If I think of more, I'll edit as needed.
Good luck, it can be a rewarding experience!
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