Need help with the correct base needed for a spa installation. Presently, we have a patio built of pavers 2 1/2" thick, with a nasty slope of 3" in 8 feet. That being said, we're thinking of building a box 8 X 8 feet level to correct the problem. We are going to fill the box with processed stone and stonedust, along with 16 X 16, 1 1/2" thick pation blocks, on top of the exitsing patio.

Will this be enough support for the spa? Or, does it absolutely need to be placed on a cement slab? We have heard different opinions, and are now reaching out to other spa owners for some good advice, before we install the new spa.

Should we purchase a spa pad that goes underneath the spa as added support?

Depends on the spa. Some need a full concrete base, others like Arctic fitted with (I think its called) a "forever floor" where you can literally put it on grass. Check out your shortlist of spas and ask each seller for more info. Failure to provide adequate support may void your warranty...