A scullery is a separate room for washing dirty dishes and storing them when they are clean along with other messy kitchen work such as prep. We really don't see them much here in middle class homes.
Sculleries (or as some designers here are calling them, "working pantries") are actually a very hot design feature in the US right now, even in somewhat smaller homes. The big trend is to build them behind an interior wall so that access to them is through faux cabinetry in the visible kitchen. Most of the time the entire kitchen isn't really bigger than a normal generously-sized country kitchen design, but about half of it is hidden. The reason for it arose during the pandemic when people discovered that having a lot of people spending a lot of time in an open-plan home meant that the noisy and messy working parts of the kitchen intruded on activities in the rest of the house, so creating a separate room that contains that without isolating the more social parts of a kitchen's function is gaining popularity.
I don't think that a sewing room really needs to be huge unless it's a production studio that will be used by multiple sewists simultaneously. What it does need, though, are a lot of good windows for light (They can mostly be high, above head-level) and built-in storage functions to contain the clutter of the "stash". In a good sewing room, the only things "out" are your machines, the projects you are presently working on and tools that are needed all the time. A table with geared pull-out leaves and a flip-up bin on one end is great for cutting projects; so that when you are not cutting you can reduce the size. (Do go ahead and have a projector mount wired into the ceiling above that area, though; projection cutting is going to make paper patterns obsolete in the very near future, much as I cherish mine.) One of the best options I've seen for a multiple-machine set up is to arrange moveable tables in a square, so that you can roll your chair around the interior of it to move from machine to machine. (With surge protectors screwed to the underside of each table so that you only have to plug one cord into the wall when the table is moved. If you want to get fancy you can have special-purpose hutches built for these tables to hold things like elastic on overhead-feed or under-table-feed reels, which I find hugely convenient adjacent to my regular machine and my serger.) I think that two generous bedrooms combined on the narrow end of a rectangular ranch design home should be plenty of space for a hobby sewist, built with two doorways and power gangs so that it's easy to build a wall between them to convert the space back to 2 bedrooms if you want to sell.
One of the best ways to integrate a serious library into a home is to build the hallways extra-wide so that they can be lined with shelving, with the plus factor that they dampen noise in the home. Articulated rolling ladders make it possible to go all the way to the ceiling with the books.
A good design for an accessible bathroom that is easy to clean is a wet room with a textured-tile floor. (I really don't recommend large open soft-goods storage in a bathroom, though; it draws mold unless air can circulate on three sides, or it's actively vented.)
OP, you might want to start by looking at plans for ADA-accessible "executive ranch" homes; you may be able to use one with only slight structural modifications, though of course, the fittings would still need a lot of tweaking. This one, for example, has a lot of what you are looking for, and I think that the side with the master suite could be bumped out further, to make room to add the sewing room.
https://www.houseplans.net/floorpla...-plan-3777-square-feet-4-bedrooms-4-bathrooms
