2 - 10.

6 - 4x4x8 + 1 - 4x4x10 + 2 2x4x8 (optional to use as extra barriers for kids on platform). Total cost was ~$80 before tax. You can check prices on homedepot.ca and search for 4x4x8 etc.

Not for this model, but there are other, bigger, Pine Bluff models.

At some point in life you'll have to take a chance - not everything is regulated. This is one of those times. The main frame of the swing set is 4x4s and they are tied together by 2.5" lag screws and cross-plates. From my personal experience, it is a solid piece of work, and I have no concerns allowing my kids on it.

No weight limits given, but the specs say for kids from 2 - 10 yrs old. My wife has used the swings (to swing alongside the kids) and has no worries.

Yes, and you should. the unit will be outside so any lumber you use should be pressure-treated. Think of it like a deck. Similarly, all screws you use besides the ones which come with the unit should be galvanized or for use in outdoor applications (i.e. deck screws).

Yes. We have the Pirate wheel and it works great (see my installation tip for this). You could put the rock climbing steps on the ladder, but my 2 yr olds can climb up the wood no problem. You'd have to install a sheet of plywood along one of the outer A-frames for the rock climbing steps to make them really useful I think - as it is now, there's not enough "real estate" to which to fasten them to make them useful. You can also get a periscope which might be fun.

The plans say 29'x22' (29' deep and 22' long). I have it in a space that's not 22' long - between two trees about 15' (the unit is 10' long from tip to tip). You need at least 3' from the rear of the back legs to provide some swing (and push) space for younger kids. As kids get older, they'll swing higher, which means having it farther away from a fence.