I assume the double doors are the entrance from the bedroom? In general, I would want to add the space to the closet, as it is relatively smaller than the bathroom, but i don't care too much for a configuration that you walk through the closet to get to the bathroom. Can you add the current bathroom layout to your sketch? That will give us an idea of what could be rearranged to accommodate a potential vanity inside the space. What else do you want to change about your current layout? What are your goals?

Sorry I'm so late getting back to you. I think that oddly sized fixtures can be off-putting. Many home buyers are looking for an "ideal" and they can't see past that. If the tub is well made and the bath is located where it's most needed a shorter size tub might not be a problem. If the bath will be used by children then its size is less important, but children grow into teenagers. acm voiced a concern I had about the location of this bath to nearby bedrooms. My mistake in calling it water-resistant drywall. It looks like drywall but it's better referred to as tile backer board. It's most often 1/2 inch thick but I have seen a Hardie brand backer that was only 1/4" thick and came in 3 x 5 ft. sections. HERE is a link to more info on these. There are several types with differing properties. On toilet location, I don't think "obstruction refers to the nearest wall or fixture. I think it refers to something directly in front of the toilet. Looking at your floor plan an angled toilet would not have anything in front of it. There might be room between the toilet and the vanity for a waste basket.

Most affordable is leave it alone. To do this remodel correctly, with the correctly waterproofed wet areas, is not going to be “budget”, even if you DIYed all by yourself. You will need to replace the window for sure. A window in a wet area is an invitation to rot. Unless it’s vinyl or fiberglass and integrated into the waterproofing system correctly. A limited space means limited options, as there are code required minimum spacing that must be followed. You need to figure out what you actually are willing to spend to get what you want. 20K? 40K? 70K? https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer http://starcraftcustombuilders.com/bath.design.rules.htm#.Wt9D4a9OnYX

Contractors do not design. They build. You need an actual K&B designer. You have a very restrictive space to get all that you want without turning it into a wet room. You, and your husband especially, need to educate yourself on modern waterproofing systems and how a wet room is properly created. The Schluter system will offer a lifetime warranty if their products are used from start to finish, including their thinset. Look at their YouTube channel. And don’t be so sure that your choice tractor can actually do this properly. Especially if he hasn’t had the wetroom and waterproofing conversation with you. Read below, and have a tough conversation with him on all points raised. https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer