Question about masks, alpha and best workflow options

Hello, I am new to Natron & I have TIFF image sequences that I want to composite; I want to keep the moving subject that already has parametric masks from Darktable, and merge a DNxHR MOV video (intermediate) background.
I have found a video TUT on loading a script to read the layers from the TIFF, hoping that that will help. Meanwhile, I am trying to find proxies that keep an alpha channel for the image sequences and can play on my old computer and the video editor, and I’ve run into problems where all proxies with alpha play horribly slow and there is a way to add an alpha export to DNxHR but I’m not sure how to do it.
Chromakey is not ideal as I have not used greenscreen and my background and subject have color overlap, but I had managed to get decent masks in most individual images I worked on in Darktable editor.
Is it best to create the composites first here in Natron then export them to compatible formats for my video editor or cut and edit my scenes, timestretch etc first in video editor then export the required sequences to Natron and then back into editor for final render?

Finally, I watched a video on Natron export (v2.3?, 2021) where he was showing workarounds for dealing with buggy exporting (write function) and that has me worried; is the export function for v4 working better?