I have sheep, but no llama, so I'll just focus on what I've found works for me with sheep. I have hair sheep (no shearing) and I keep a miniature donkey with them as a guardian animal. I don't seem to have a lot of predator activity, so I don't really know if he's effective or not, but I haven't had any predator losses yet.
As far as the poo issue, I wonder why you wouldn't want it in the grass where it can do more good? Sheep manure in my
experience is dry and nearly odorless basically 100% of the time. If you are doing high density rotational grazing the
boost in soil life will make sure your manure load vanishes in hours or at most days anyway, and only about 10% of your pasture will have animals on it at any given time.
For containing them, I don't use poly tape so I don't know for sure how much you'd need, but Greg Judy (in "Comeback Farms") I believe says he can contain them with 2-3 strands for inter-paddock divisions and a 5 wire high-tensile perimeter fence. I use electric poultry netting for mine, and just pick up the paddock and move it around the place every day or two (takes about 20 minutes to move the fence). I don't have a perimeter fence yet, but I'll be putting in high tensile electric this winter if all goes well.
I'd recommend getting the best charger you can afford. I'm a little suspicious of the $50 model you linked to, though I don't know much about the brand. The charger is about the most important part of your fencing system, so it's really worth getting one you can rely on. Look for higher stored
energy (0.2 J on a grid-powered charger is really low). I use a Patriot P30 charger from premier, which is rated at 30 miles of fence and 4.6 Joules. It's $168 on premier1supplies, and it comes with the option of hooking it to a battery/solar system with no special gear or modifications. I've been happy with it so far, but when the ground is wet with lots of weeds and I have 4 sections of netting, the shock does get pretty weak. I'd be afraid the animals would not respect a smaller amount of energy.
If you get hair sheep, they are super hardy. They can be outside all year long without shelter, though I'd recommend giving them a place to get out of the sun/rain/wind/snow etc. My shelter is currently a bent piece of
cattle panel with a tarp on it, and they seem to love it. I'll be building them a better hovel for the winter, but the cattle panel option is nice because it's very lightweight and durable. Hair sheep don't need worming, hoof trimming, shearing, or other interference in general. They don't need help lambing or mothering. They're great animals in my opinion, and they're a hoot to watch, too.
If your 4 acres is lush grass and broadleaf forbs, you could probably get 6-8 sheep per acre on it. If it's not as lush, you'll do less. I think the best policy would probably to start out with a conservative number and add or subtract as you see how they progress through your pasture. You'll get a lot better pasture improvement and more carrying capacity if you do high density grazing (i.e. holistic management or MiG). I'd highly recommend getting your hands on a copy of Greg Judy's "Comeback Farms" if you can manage it. The book is jammed with practical experience and useful tips, especially regarding fencing.