I don't know much about hot tubs, but I do know about building. I'm a woman who can handle her power tools!
It's all about your site. Since the site is everything, my answers are rather general.
1) are you talking 1" X 6" or 2" X 6" pressure treated pine? Some people like the engineered wood...but I don't like it at all.
I recommend 2" X 6" pressure treated pine whatever route you take.
2) what kind of soil do you have and are you on a slope? How do you plan to secure the gravel? Gravel alone shifts and washes. Are you talking about putting a frame down directly touching the ground, then filling with gravel? I wouldn't want to do this for long term unless the site conditions were perfect and you live in a dry climate with clay based soil.
3) There are brick pavers and there are BRICK PAVERS...
some are "sidewalk" grade and some are "driveway" grade.
the driveway grade is made from concrete with fiberous reinforcement in the mix.
Only the reinforced concrete is suitable for good long term support.
The sidewalk type pavers are not reinforced and will crack, it's only a matter of time.
When pressure is applied, they can crack immediately.
Above ground platform with minimal board cutting....
For an above ground platform measuring 8' x 8' or even 10' x 10'... decide the size and use precut pressure treated pine boards in that length and 2" thick. To build a square frame, use 4'' x 4" pressure treated corner posts. Boards: Five 2" x 8" (or) 2"x 10" pressure treated pine decking, with the extra beam down the center. Approximately three 2" x 4" PTP boards for cutting into short lengths to brace corners and center beam.
Depending on your site whether or not I would dig a footing or simply use the pre-fab footing (ones that hold a 4" x 4" post). Home Depot or Lowes has the pre-fab concrete footings for decks.
Good luck,
Bama