I got a prompt, detailed reply. It really showed the differences between Envisioneer and 'Classic' FP...
To summarise, IIRC, Big_E cannot import doors, windows or fireplaces into 'wall-cutting' categories per 'Classic' FP, but has remarkable door and window design-tools. Also, imports may be 'snapped into' wall, and openings added if required...
Okay, that would seem to bury any chance of TFP getting 'wall-cutting' imports.
D'uh...
Okay, I'll probably download TFP trial at end of January, make some doors and windows, stress-test the file-capacity etc before I commit to TFP_Pro and that total re-draw. With a bit of luck, the FP-import filter may arrive in time...