All,

After some research I came to a conclusion that in the USA, there is
no legal requirement to use a weak link during a ground launch,
regardless of the rope/wire strength.

First question: Am I missing something? Is there something like a
ground launch version of 14 CFR 91.309?

Second question: If the glider's POH does not offer any guidance (say,
1-26), what would be an appropriate range of rope breaking strength?

Thanks!
Bart