Welcome to the forum @rnx.
I don’t see a single question in your post, but I’m going to answer anyway.
You can read up on some prior topics about this with the tag #hardwarekeyboard.
Though if your current phone will survive a few more years there is a chance that the FP3 will be out then and that could be a whole different story as to which keyboards will be compatible and what issues they might have.
Also in case you are wondering: I’m pretty sure the FP3 will be a touchscreen device too.