Just remember when dealing with fish hooks the larger the number the smaller the hook. Try looking at some of the size 18 or 20 Gamakatsu single egg hooks for the wall anchors. Gamakatsu hooks are a little pricey as they are topnotch in quality, but to get what you are looking for I think these will be your best bet. Just be careful with these things. They are designed that as soon as the point touches fish flesh, just a bit of pressure and they will sink right in. YIKES!
For the clothesline I would just fishing line. Again get quality trout stuff. Avoid Maxima. White Maxima is strong and good for area's with lots of rocks and fast moving water, it has alot of memory to it, and won't realisitcally sag. I would recommend Berkely Ultra Thin, or Extra Limp, from the Trilene series. Just a small spool of this, or spool of leader will work fine.
If you need something that looks like fine braided cord or rope, check into Spiderwire. It is multifilament braided kevlar line. Strong and cool looking. Has a definate scale appearance for many things.
As a fisherman who has gotten pretty heavy into it(I used to spend 9 hours a day 7 days a week for 5 months out of the year fishing for trout, and then more time fishing for salmon and steelhead), I've gotten pretty intimate with what the advantages and disadvantages are of different equipment and what will work for scale modeling. I hope this information helps you in your endeavers. You can also take this info to a tackle shop a REAL tackle shop, and see if they have any extra lying around. Like maybe the last 3 or 4 feet from a spool, that sort of thing. Explain you don't need much and what you need it for. They might just be willing to give you the leftovers, or some used stuff that would still work for your purposes. Remember any good fisherman changes out his line fairly often. If looking at the used stuff or the disposal bin, just be sure to check how thin AND how limp the line is, you need it to be limp with very little memory. Again hope this helps.
Michael