Patons Ritz yarn was a bulky yarn. It was about 12 ply.http://www.ravelry.com/yarns/library/patons-ritz
because its pertty
This does not seem to be a current yarn. I suggest you contact Paton's via their website.
Weight: Bulky / 12 ply (7 wpi) Gauge: 16.0 to 18.0 sts = 4 inches US 9 - 5.5mm
Patons has many weights of Tweed wool, so look through the Paton link and see if you can find the specific wool you are looking for and have an answer that way.
It appears by looking at the Patons link I attached, that this yarn is still available. If you don't know where to find it in your area, contact Patons and they would be able to direct you to an online or retail store in your area. (at the top of the page of the Patons link, is a Store Locator tab that you could also click on).
The difference between 8-ply and 4-ply wool, can depend on the weight of the plies. Some 3-ply yarns have heavy weight (fatter) plies, which knit up heavy worsted, where 2-ply lace weight yarn plies are much lighter (skinnier) plies that knit up very light/lacy/small.If I were to guess, the 8-ply in question, may have smaller plies than the 4-ply. I think if you double the 4-ply, that would be too much. You should try a gauge swatch using the 4-ply singularly, and maybe adust the needle size.
Working with 1 ply wool is not easy. It takes forever! The simplest thing is a scarf.
Yes, probably.
Patons
I searched and was unable to find Patons Camelot Wool. The best I can figure out is that you might be referring to Patons Kroy Socks FX in Camelot color. So, going by that thought, it would be a sock-weight yarn; or category 1 fingering weight yarn. Therefore having a ply of 4. If I've totally misunderstood what yarn you're asking about, I've attached some URLs which might help you to translate the information you have on the yarnband into ply.
See http://www.YarnStandards.com for how the categories of yarn weights compare in terms of relative gauges and needle sizes used to achieve those gauges. Worsted weight (Category 4 - Medium) is the yarn commonly used to knit sweaters in the U.S. U.K. knitters often use a slightly thinner yarn called "DK" (double knitting), which falls into Category 3 - Light. Worsted weight yarn is typically knit at 20 sts/4 in or 10 cm on US 7/4.5mm needles, whereas DK weight yarn is typically knit at 22 sts/4 inches or 10 cm on US 5/3.75mm needles. Some countries still use the old 2-ply, 4-ply, 6-ply, 8-ply classification to describe yarns, where 4-ply is fingering weight, 6-ply is sport weight, 8-ply is DK, and 10-ply is worsted weight. One problem with that system of classification is that it assumes a standard ply weight. There are many yarns these days (particularly in the Bulky and Super Bulky categories 5 and 6) that are single-ply yarns which knit at various gauges on various needle sizes.