Well.........you had a pretty extensive and specific list of needs and wants. I assumed (wrongly) you knew you were going to have to pony up.
Sure $700+ is a princely sum, but 3-$400 of that is batteries and charger. Factor in the tool activation trigger, variable speed , the cleaning accessories and adapters, plus HEPA rating and it’s not outrageous. But, if you won’t be adding anything else in the Makita lineup then that 400$ is dead weight. The 120v operation is a unique feature too, but you’ve said that is a drawback for you.
re: only needs one battery. Im sure you understand how battery works; so realize One battery isn’t a plus in the case of a power hungry tool like a vacuum. Especially when weight isn’t a concern.
Brad - your system doesn’t really make sense. Either you don’t really have 5hp “dust collector” or you’re starving the impeller of air with 3” pipe / hose and are cooking your motor. Now a 5hp craftsman shop vac could run on a 3” hose.