I don't know about hole sizes because I don't string my pearls myself, but there should be knotting between pearls, to prevent the pearls from damaging each other by rubbing together. (Or, there are some little bumper bead things you can use instead of knotting but I don't know the name of them).
I plan to have my necklaces that aren't already strung on PowerPro restrung on PowerPro (which is basically fishing line) and also with "mystery clasps," a screw mechanism fitted into the two end pearls instead of a clasp.
This is because I'm tired of having to have my pearls re-strung every few years even if I don't even wear them. The gimp (the wire coiled around the ends of the stringing material, which then attaches to a clasp, for any who don't know) is usually the first thing to go, maybe because I usually request my pearls be strung with PowerPro in the first place. The gimp flakes off and gets icky/black. I figure that with PowerPro and mystery clasps (and no gimp!), I shouldn't have to bother with re-stringing any more.
However, the end pearls have to be a minimum size for a mystery clasp, maybe 8mm?
Also, if you use PowerPro, it makes smaller knots than silk or polyester so the finished strand will be slightly shorter. (The finished strand would also be slightly shorter with a mystery clasp).
I also really like "endless strands" for rope length, one continuous strand (on PowerPro) with no clasp (or gimp!)
Umm, I think I only answered one of your questions but that's all I know.
ETA: Another thing about pearls is that they shouldn't be left in a safe or safety deposit box for extended periods because they can dry out and crack. That can become a real PITA in certain situations! Sorry for blabbing on lol.
One more thing I like about endless strands or mystery clasps is that I'm kind of picky about having my metals match and that way, there isn't any metal so they go with anything.
...And, you can even get several mystery clasps to have the same strand used as bracelet/s or different length strands or double/triple strand. Woo hoo!