Issues with a large smoke simulation

[DMNS]

Hello everyone,

I have been attempting to figure out this problem on my own, however I have spent far too much time on it and would love some help if I could get it. It would be very much appreciated.

I am attempting to create the effect seen in my first image, the very odd colored smoke.

The second gif is what I currently have, which I would say is a good 70% of the final look for about the first third of the chunk of smoke.
I need to create the next chunk of the effect, which is the larger more diffused, bigger turbulent smoke. I have been attempting various methods to achieve this.
I have tried to use control fields on the current simulation. I don't think this is the best way because my GPU runs out of VRAM, and also I have less control than if I were to break it into multiple sims.
I also tried copying the first VDB, clipping, transforming to the XMAX of the first VDB (where the next part of smoke should start), scaling, and retiming, which sort of worked from certain angles (not my camera) and I felt it was sloppy. 

So now I am wondering, what would be the best method to break this into 3 simulations? First part is fine, the tight, high frequency turbulence that I am happy with (happy to fine tune it later). 
Now second, the middle chunk of the bigger poofier part, and then finally the tail end.
Maybe this could be done in 2 simulations. Maybe I would need 3.

Would I want to source in from the same direction the first simulation is flowing outwards? I am not sure how to proceed efficiently and would really love some help!

Thanks!

Edited January 29, 2020 by DMNS
Added more details