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Things like sizing the pump for the size of piping and the quantity of jets will need to be considered.
A lot of spa companies wing it.
On the general topic of seating I just want to put an idea out there. Last year while on vacation I used a swim spa that incluced a bench seat lounger made up of stainless steel tubing (about 1.5 inch tubing on 3 inch centers running length wise down the reclining bench) The main problem I had with it was sliding side to side from the jet action, but the pipe spacing did allow water and bubble flow from beneath.