Freeform with 21c vs. Essbase 21c?

Summary:

I'm engaged in a situation where there will be a large (24+ dimensions) ASO cube in play, one that will potentially grow to have one or more very large (500K) dimensions. Also in play is a BSO "lookup cube", which we will use for rate/cost calculations based upon volume data pushed from the ASO cube, the results then pushed back.

We're considering both Freeform (which the client owns, -test is 21c) and Essbase 21c itself. If we go Freeform I expect this BSO cube will need to be in its own instance because we'll run out of allowed dimensions. I do not envision using many of the EPM platform capabilities, though some Forms could be nice, but no Smart Lists, Tasks, etc. Data Management/Exchange) is already out of play because of the limit (20) of UDx fields available.