first off, assembly. it was much easier than we expected. (not easy, but easier than expected) you probably need 2 adults for some of it. but could be done with 1
we assembled it in 30-45 minutes I think.
second, size. I have 3 kids, age 10, 5 and 2. they have all jumped on it at the same time and enjoyed it. I think it would be ideal for 2 kids jumping though, just so they don't hit each other. but 3 small kids can fit. I have had 3 10 year old girls jump on it and they were fine also.
also, my oldest is a gymnast and she is able to do many of her tricks on this trampoline. it's just big enough. she has said she wants our next one to be bigger though for gymnastics purposes.
so, I would say this is ideal for 2 kids jumping, ok for 3 kids jumping (if they are mindful about not getting too close to each other), and only 1 kid at a time for doing flips and things.