what are the benefits of a skinny string? and what would be a safe number of strings for a 55# recurve?
Depends on who you ask and what you are comparing them with, and probably what bow you are using them on.
I've been making strings for around 20 years, and quit counting long ago at around 10,000. Not that I'm any kind of expert, but I do have better than average experience with strings.
In my own comparisons, I've found no real benefits when comparing a "skinny" (low strand count) string
with an equally well made moderate strand count. I've compared them on a longbow (moderate deflex/reflex) and selfbows. Dont' remember if I tried one on a recurve or not--dont' think I did, after seeing no reason to based on the results I already had.
Negatives are increased stretch, increased creep, and decreased durability.
The minimum number of strands also depends on who you ask. If you ask a manufacturer like BCY, you will likely get an answer that is about double the number of strands that some are using.
I don't care for a way overbuilt string either. There's normally a happy medium for most materials, and with the way they are improving there's less and less need to go with extremes in either direction--at least that I can see.
This is just my opinion, my thoughts, my observations. I don't claim to be any kind of expert. Your results may vary.