no, there is no cut off. And I cannot promise, that all of the wanted plants will be available. Must visit first the different nurseries. After I have seen the stock in those nurseries I will be able to tell more.
So just go ahead in making lists. On the end I'll count together an go for looking. And, of course, there will probably more cultivars than the wanted in stock.
And there isn't a cut off in how many people can participate to that. No matter if there are 20 ore 50 or 100 members.