Which cv's can handle strong sun.

Yes, they sure can build up. In Richard Johnson's case he decided hybridizing was what he most wanted to do and in Tahiti there is never a winter set back from cold so he found he could make crosses year round and germinate the seed whenever he wanted. A large portion of his plants are seedlings he grows in smaller pots. There's no way 2000 mature bushes would fit on a rooftop but it's not a stretch to get that many smaller pots. He's lost a lot of plants over the years, too, which has the plus of giving him more space for new ones.

Probably the worst thing anyone can do when growing hibiscus is to grow more plants than you can handle. The first very generous guy who gave me wood to build a collection had about 400 hibiscus in pots in his yard but found he could not water, fertilizer, and repot that many and so they rarely bloomed and he lost a lot of them over time. I think it's much better to only grow as many as you can take care of well - much more satisfying results that way!

That said, there are ways to manage larger numbers. A drip watering system that runs on a timer and that has a fertilizer injector providing constant feeding is probably the number 1 time saver. They are not hard to set up but allow for almost an unlimited amount of hibiscus to be grown with minimal effort. I helped Dick design his watering system and although he had to cobble it together from locally available parts it does work and even allows him to go away for weeks at a time on vacation.

Charlie