I agree about the J15, but the D16 is also a nice-looking engine, I think. Still waiting for someone to produce a RTR E4. Might be waiting a while!
It's nice to follow someone's progress. I think how much internal lighting, etc, you do is very much down to what you want to present at the end. If you want to have a very detailed exhibition layout, for example, then a lot of detail helps to focus attention when there's little happening. Personally, I like internal lighting in buildings anyway, because winter or nighttime running is definitely enhanced by it.
My Suffolk branch is dragging along, but other commitments (even in lockdown!) get in the way sometimes. Also, a malfunctioning point held me up - I'm using handbuilt pointwork as I prefer it to Peco track. It was glued down, but had to be removed and was damaged in the process. By the end I had almost entirely remade it!