I have all brothers and use the same foot on both so I am not sure how you adjust sea allowances on both

I have pieced all my blocks with one machine (Singer Featherweight) and then put it all together with my Janome 6600P. No problem doing it that way. I think I might have had some issues if I tried to piece the blocks with different machines.

I use a Singer 301, a Singer 404 and a vintage 15 clone on any quilt I make. I can recognize a 1/4" seam and never have a problem switching machines. I rarely have to trim a block except a HST one, but that's a planned trimming.