Ahoy Jim,
AB is short for able bodied seaman, the step up from wiper. (Don't ask, but that was my first z card.)
Shock loading on halyards is most rare but a gaff peak halyard can get quite a strain during a gybe. When one local fleet finally moved from manila to dacron, they had the halyards set by feel like they had with the manila. In a good wind the loads up there are impressive and you'd see bending gaffs commonly, sometimes breaking just under sail. Setting the peak that hard with manila worked well enough since in a gybe the line would gather back some of the stretch and let it out the other side. Dacron was just enough less stretchy that people had to learn to trim the peak halyard a little less belligerantly.
Good sailors can spot folk with nylon sheets a mile off and it's painful. You really will have so much more fun with your boat if you do her the honor of letting her sail right. A gybe is the only time the shock on the sheet matters much and the risks are way over-rated compared to everything else that can go wrong. For example, when the wind gets on the other side of the sail, the boom naturally lifts. Absent a heavy boom or a vang, it can easily lift high enough to foul the backstay on the way across. No there's some shock loading but it's not on the sheet.
Many contemporary sloops have the main ending with a cam cleat mounted on the exit tackle, which is often on a track. The cam cleat needs to be angled such that when you're hauling in the sail at the start of your gybe you're not hauling through the cleat. Once the sail's coming across you want it running freely. With a little practice and maybe some gloves if you don't harden your hands with rowing or rope climbing or something, you should be able to haul in fast and when the sail crosses do NOT hold the sheet to then let out. Rather, have your palms open so the sheet can run and you grip it only when it's moving. That way the only shock is overcoming the sheet tackle's initial inertial resistance.
There are various boom tamers on the market but it's worth just learning how to handle and surge the line.
It's also useful to remember the the shock is rarely that big a deal. The boat will roll with it and modern dacron in the sheets and sails are incredibly strong.
Line size - you don't want it too big for the boat but most main sheets are fantasticly stronger than the job requires since the hand grip comfort is paramount. I find line smaller that 1/2" annoying. For a genny sheet, 5/8" is hardly too small.
G'luck
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