On your later points, see @sartoric’s directions but as to on-board Topographic map - nope.
And FWIW, I also use the thing for hiking and would also like to share your beliefs about FusedAlti but it hasn’t been my experience (on hills) that it’s much better than the Baro on the old Vector. Weather change might require the Vector to be manually corrected (of course) while, regardless of weather, the GPS component of FusedAlti could introduce its own errors, overriding manual correction.
If your search yields simple, useful answers to your questions, please drop 'em back here and thanks in advance for the gleaning.