I don’t usually like to tell people what to do (because they don’t listen anyway) but hey, I’m in the mood, so take this for what it’s worth.
Video equipment gets obsolete very rapidly. It is very difficult to “invest” in it with a longer time horizon than 2-3 years, if that.
There are two “equipment philosophies,” both valid. One is to buy the hottest gear, spend a lot, & sell it rapidly (before it has depreciated too much) so you can buy the NEW latest-and-greatest next year. The other option, which you seem to be pursuing: “invest” in the most reasonable cost-performance-ratio equipment that you can find, keep it a long time, and accept that you will not get much for it, if anything, when you sell. This requires considerable research and no small amount of luck. I think if this is your path, you should be looking at video cameras, not DSLRs, because that market is more mature and stable. Video cameras are going to be a lot more useful to you, there are a TON of great video cameras out there, and they will still be useful several years from now, whereas the newest DSLRs (a year from now) will probably make the current crop look inadequate, imho.
If you decide on Option 2 then you should also try to save yourself a lot of money by getting to know somebody who is pursuing Option 1.
The “buy the glass” idea is good, but it really belongs to a different era, when lenses didn’t offer all of this advanced automation, aberration correction, etc. and “glass” was more easily transferable between various PL-mount cameras. I don’t think anyone can predict for certain which CAMERA manufacturer will have the winning hand in this market, five years from now, so investing in a lot of glass is problematic, and may even lock you into a path that is not optimal. I know too many people who feel “stuck” in a certain DSLR line, because they bought a lot of Nikkors (oops) years ago. Yes, there are adapters, but they don’t generally offer the complete package of electronic connections that “native” glass will.
So my unsolicited advice is to buy a good, cheap, used (or even new) video camera for next to nothing, let the DSLR or 4K or whatever market sort itself out, and concentrate on the main thing: your skills, not the impossible task of predicting the unpredictable.