Awesome pictures Ward and we’re super excited to see your project take shape.
For that size bathroom you might want just a dedicated vent fan that can pull all the steam from the shower outside. We do have a video with Bill White in the Electrical section where he talks about the different vent fans and Pros/Cons. I know he mentions those dual recessed light/fans but can’t remember his opinion, lol.
Converting to PEX is very easy and we do it for many projects. Just check your local plumbing codes to be sure you can use PEX. Many of the mixing valves will easily adapt to PEX as well.