That explanation is actually really useful.
The point we didn’t make before is that there are thousands of items (on envato alone) and unfortunately, it’s impossible for anyone to be properly aware of all the options. We’ve bought 1000+ yet we’d still not be able to give trusted advice beyond a fairly narrow (maybe 20-30 items) selection.
Based on your description above - this really doesn’t sound like something that you should be basing on a stock theme.
With respect, the above sounds like you are expecting/looking for the ideal solution that ticks all the boxes to some extent, straight out of the box? Stock themes don’t work that way.
Given the fractional price being paid for something which should easily be 10’s of thousands of $, you have to be willing to compromise and adapt. As such they do not suit perfectionists!
it sounds like a lot going on, which almost certainly won’t be covered by one stock theme
more things going on = more to break. Dedicated build = less that can go wrong.
stock themes are by default bloated with numerous features to make them more versatile (this is probably a reason why you haven’t found the ideal one yet as it probably clouds your judgment??).
You are going to be handling a lot of quite serious data so need to be 100% confident in the security (not to mention invest in some decent and therefore more costly hosting).
If you use a stock theme and the author stops supporting it - then what? A freelancer/agency will charge a lot more to work on someone else’s code, and there’s greater room for error.
If you are serious about doing a site (esp. one like this) properly then you have to invest properly in the build, support, hosting, legal, security etc. No one will come and use your site if it looks amateur, hacked together or unreliable.