I have a few questions.

Is this is a stand alone spa or part of pool/spa combo?

What is the material of the spa-fiberglass gunite?

Any spas we plumb, whether a stand alone or part of a pool/spa combo, have a 2 pump system.

On a stand alone, there is a separate pump and filter for heating and treating. A separate jet pump is only to provide water to spa jets. We NEVER use a filtration pump as a double duty set up.

On a pool/spa combo. the filtration system is shared with the pool. Here too, a separate pump is used only for the jets. We install automated systems that allow changing from pool to spa mode.

With that being said, the pipe size you intend to use is way undersized. Most of our spas have 3" suction and 3" return for the jet pump. Some situations require larger pipe, which is dependent on factors such as distance and the number of jets.

The plumbing manifold for the jets is set in a looped fashion to provide even distribution of both water and air. An air blower can be used for additional bubbles, but if the plumbing is set correctly, ambient air drawn through the jet assembly, which will also provide bubbles. The pipe size is reduced spa side to accommodate the jet assembly.

Jets should be based on a 10 GPM requirement to each jet. So 7 jets should have a pump that can produce a minimum of 70 GPM. There's a formula to calculate this. It's based on distance, GPM requirement and calculating number of fittings from point A to point B.

For the filtration, a minimum of 2.5" for the suction. I would run 2.5" for the return and reduce at the spa.

Consider a variable speed pump as well for both filtration and the jet pump. By July 2021, the Department of Energy (DOE) will require variable speed pumps for swimming pools and spas, We have been installing VS pumps for about 10 years and currently on new builds. 2 speed and single speed motors will not be produced after July next year.

The larger pipe reduces friction loss, decreases water velocity and provides a better supply. 1.5" is WAY too small. Your proposed pump is way oversized for your proposed piping.

I've told my clients this analogy when using too small a pipe. It's like sucking water through a cocktail straw. The pump will starve for water and you'll never get the full benefit of it's capacity. And, the pumps longevity will be compromised.

Mind you, this a pretty general calculation based on my experience for a "typical" set up.