Doesn't seem like he says exactly what string set it is. Seems like it was custom, not commercially available (unless I missed something)
Because there isn't one. A ukulele is strong enough to take being strung, or it isn't. If it isn't, it was either built wrong (in which case you're flogging a dead horse) or there is some damage that needs to be repaired before you use it or you'll cause more damage.I'm sure it would be ok, it's just strange to me there isn't a go-to answer or set of strings that people with antique/frail ukuleles use. I know a lot of people play them. I've done lots of research and there just isn't a clear answer.