40 sq-ft is 7' round diameter and 10 people would be pushing it. Even 8 is a little cozy. Plus most everyone will want their own spa jet so I would say 6 people is a practical limit.
As for heater size, I would go with a 400k BTU heater which is what I have. This will increase the speed at which the spa is brought up to temperature so there isn't as much wait time for the spa to get hot.
As for a pump, the plumbing will need to go through the filter and heater both of which add a lot of restriction. Depending on the head loss in the equipment, the VS may or may not be able to provide enough flow rate for the jets so you might want to also have a bypass built into the pad just in case. In most cases, I prefer to have a separate pump on separate plumbing for this reason.
Forgot to mention that I would go with the new VS (011018) over the 3050. They are about the same price but the new VS has several more features.