Adding a IG spa to an IG pool

Does anybody have any experience adding a IG spa to an existing IG pool?

I'm a DIY kinda guy--but digging a big hole next to my pool scares me. I'm in socal. If anybody has any advice or any recommendations on who to talk to--I'm all ears!

You can add a spa to your existing pool.

Will the spa be built within the pool perimeter?
Will the spa be built outside of the pool perimeter?
Will the spa be built partway into the pool?
Will the spa be raised or at pool level?

Pool spa combo with same equipment with spa spill over?
Pool and spa with separate equipment and no spill over?
Pool and spa with separate eqiupment and spill over?
Pool and spa with separate eqiupment and water feature from spa wall?

Will the spa be built within the pool perimeter? Didn't consider this an option
Will the spa be built outside of the pool perimeter? <-- preferred
Will the spa be built partway into the pool? No
Will the spa be raised or at pool level? Would like it slightly raised so that I can have a waterfall spillover into the pool

Pool spa combo with same equipment with spa spill over? Yes, but need to add a heater, a blower, and maybe a boost pump?
Pool and spa with separate equipment and no spill over? No
Pool and spa with separate eqiupment and spill over? No
Pool and spa with separate eqiupment and water feature from spa wall? No

I just haven't found much info on anybody doing this. I'm considering just buying a AG spa and having it seperate. The only pricing I've heard was in the $30k range--which was really funny!!

I would imagine I'd probably have to drain the pool to add the spa. The idea of digging a big hole right next to the pool--I'd think there would be cracking issues. That, plus the gas line is on the opposite side of the yard, and would require a lot of work and trenching through concrete to get it over to the pool equipment--makes me think AG prefab would be a lot cheaper and easier.