I tried to hide the window unit on my shop with a trellis that was 18" from the back of the unit. The heat burnt up three different vines, a Spanish Flag vine, Mexican Flame vine, and then a Blue Sky vine. There is a lot of heat coming out the back of a window unit. I finally decided I would rather have a vine covered trellis than have the AC. I put an exhaust fan in the gable at the back of the shop and just leave the doors open when I work in there. It's still very hot, but I have the vine. Jim

"Spackle" is filling holes by DIYers. This needs mudded minimum 2 coats which is considered drywall "finishing." The painter should not be relied on for that trade, but some may be artistic enough and don't mind doing the work for extra pay. The 1/2"+ filled gaps will probably invite a crack or two over time, as you get those anyway even when you put drywall sheet butts at window corners. LOL also I've never seen anyone go for the look of Venetian Plaster on top of colonial casing. Spillage on the baseboard heat as well. For such simple work, not professionals by any means.

Depending on what else is going on in the room (or the rest of the house), I think you could make the apron under the stool extend out for the casing sides to set on top of - if it's only this one window. If there are several areas where you are modifying, then maybe change to a more traditional or transitional style. You need to have a plan that is cohesive all the way through. Any possiblity of redoing this stool or "adding on" the needed extensions in marble? When it comes to trim (or other details!!), you have to start with the total finished look to be able to get there! Ask me how I know!

Are the pictures the existing situation pre remodel? What is the opening to the left of the vanity? It looks like the vanity is encroaching on this opening? What are your plans for vanity placement? Because it doesn't look like you have the room to spare for any padding of the wall as I suggested earlier... The toilet isn't a big problem--you can use an offset flange to gain some space behind the toilet. Or purchase a different toilet based on how much rough-in space you have. Toilets are available with different rough-in sizes...10", 12" & 14". The opening left of the vanity could be the larger sticking point. As far as actually padding the wall--don't worry about that. Pretty much 101 beginner DIY. If you don't already own a multi-tool (oscillating tool), get one. That tool makes so many difficult, near impossible jobs so, so much easier. Like cutting back window jambs.