Any idea how to update exterior to incorporate the addition and update the existing exterior?

What are the exact measurements? I think you already know the answer, which is that keeping it maintained in that tight of a space is going to be nearly impossible. Because it's inside the shower, it will constantly be getting wet, which means it will constantly need to be cleaned. If it's not easy to maintain, it's not a good design. I would say 12 inches would be best to aim for around the tub, some people are okay working with smaller. Just know that the smaller the clearance, the harder it will be to clean.

Yes that's a valid concern. What do you think of a back-to-wall one? It looks less pretty but perhaps more practical, like this: https://www.build.com/anzzi-ft-az112/s1437914?uid=3386153&jmtest=gg-gbav2_3386153&inv=1&source=gg-gba-pla_3386153!c1714063357!a64501153102!dc!ng&gclid=CjwKCAjwxev3BRBBEiwAiB_PWHZuegA42JN6wH4TRvIbAOb_9BK9FbU58jv69hlbxNx4jP2Qbm6vJRoC8EEQAvD_BwE&gclsrc=aw.ds

I'm in the middle of renovating a small bath in a prewar 1930's building. Our's is a tad bit smaller, 91 x 58, so I'm jealous of your extra inches! Your layout is great. Here are some thoughts: Tub You say you love a batih. Is this going to be your bathroom where you shower, or do you use the ensuite? We are likely going with the Bellwether because it is a classic look and the low height makes it easier for my arthritic parents to step into. However, that low height makes it not a great option for taking deep baths - the water depth is only 9". If this one doesn't work, there are other deeper ones. Cast iron is a must for a good bath with great heat retention. Many people posted why I should not go with glass surround in my tiny bathroom: You'd think being glass it would disappear, however, I think glass looks clunkier in a tiny space, even if it is frameless. A shower curtain when left open makes the room feel much bigger. Glass is hard to clean and even moreso in a small space. Toilet You are not going to knock your knees on the tub. You have at least the width of your door between you and the tub. Get an elongated one. They are so much more comfortable! I had Toto's in our old house and they are great and have a powerful flush. Depending on the look you are going for Promenade could work. Sink Do you need much undersink storage in this room? If not, I'd get a console sink with chrome or glass legs. It gives a much more open, simple, and classic feel. I find that pedestal sinks limit the surface area because they have a rim around them. You can get console sinks with a flat top so there is more room for soap, toothpaste, whatever. If you do need some storage, we have a wall hung vanity with two drawers in another bathroom of ours. The millwork has a somewhat classic vibe that was made more so when I put in classic knobs. No matter what sink you use, a round bowl in a square or rectangular top will yield you more surface space than a square or rectangular bowl.