I don't sew in the kitchen, though I used to sew in the laundry room. When I was renovating, I did build the sewing machine into the cupboards.
It wasn't done, like the old machines where the machine turned on it's side into the cabinet. Rather we cut a hole in the countertop, inserted the machine, left it standing. Then had a clip up/down lid with a skirt on it, so that when it was closed, the machine was fully enclosed and the countertop looked consistent with the rest of the laundry countertop, except for the cuts in the arborite.
For my "chair" we built a cube with shepherd's casters that fully fit the hole where your legs go, so that when not sewing, it was out of the way. The top was padded so it'd be nice and cushy, then it flipped up for storage of sewing needs. There was a lift out tray so it was double decker, rather than one deep hole. There's lots of improvements that I'd do if doing it again.
In one of the drawers in the laundry cabinets, there was a flip out ironing board. It wasn't a very big laundry room and this all worked out well.
Limitations ... if you siwtch machines, the hole wouldn't likely fit, though you could easily renovate for the new machine! Space wise I was limited because of the built in. In other locations, one would be able to have an open end, to allow the fabric to drape down an open side (*think* fully assembling a quilt)
So yes, you have the starts of a fantastic plan ... take your time to plan it out and you'll be more than happy with your results!