Your suggestions are spot on. I have been using your version 2 (MBP plus external displays when in desktop mode) since 2017. Then on a recent month+ trip running an out of town project I carried the MBP plus one external display. The Studio + portable display for such travel would work.No, obviously the option will need electricity access. In all of my travels- quite substantial for business- I've always been able to get some electricity when needed. Personally, while I have desktop, laptop and iPad, I find the places where I'd have to depend on a battery- like flying- is too cramped for MB anyway. So I use iPad in such situations. Home office: I'd have electricity. Client's office: I'd have electricity. Hotel: Electricity. Etc.
However, for those who worry about such stuff or actually DO lean on battery a lot of time, my suggestion would be to do the other variation of the same idea: buy MB (and no desktop Mac) and a great desktop monitor, keyboard, mouse and use the MB for BOTH purposes.