The others here can answer about InDesign specific needs, though at 256GB and 16GB you have 100x the storage requirement and 8x the RAM requirement. It's even 2x the recommended RAM. If you were also running several other CC apps at the same time I can see how 32GB would be better than 16GB, or that between them all they may benefit from more internal SSD space.
But about the RAM and the SSD on the newer MacBook Pros, they are apparently soldered onto the motherboard. You have to make the decision about how big they are now. I'm also about to go from a mid-2015 MacBook Pro to one of the new ones, I haven't finished thinking it through yet, but I will probably get 1 TB SSD and 32GB RAM. I have 1 TB SSD on my current machine, and it has been useful. I can't decide whether to pay the extra money for 2 TB, on the assumption that during its lifetime I'm likely to need that much space.
Colin Smith did a review of the new MacBook Pro a few days ago, perhaps some of his thoughts will help:
2018 i9 MacBook Pro Review for Creative Pros - (with heat fix) - YouTube
@Colin: I assume you are referring to Adobe's system requirements. I don't consider those are not "real world" specs--just enough to do basic jobs. 2 GB is a joke. 8 GB will certainly work, but for large jobs, most likely the hard drive will be used for RAM cache. That could be bearable with a larger SSD drive but not optimal.
The job in question will certainly work on a 16 GB system, but I would go with more RAM since a 512 GB drive could be supplemented with external drives. (My loaded Mac OS and programs take up less than 100 GB.)
Other Computers
I like Macs (since 1985 and former Apple certified consultant), but realized a long time ago that computers are just tools and the Mac OS and Windows OS operate basically the same for most users. See: Macintosh and Windows Cross-Platform Tips for some tips. (I have both a 15-in MBP and a 15-in Dell XPS.)
Since you expressed interest in other options, I like the XPS 15. With the same processor (8th gen. i7), here are the differences:
MacBook Pro with 32 GB RAM and 1 TB SSD: $3400
Dell XPS 15 with 32 GB RAM, 1 TB SSD, and touch screen: $2600
Dell XPS 15 2-in1 with 16 GB RAM, 1 TB SSD, and touch screen: $2600
I always buy addition 3-year warranty coverage for my laptops, the costs between Apple and Dell are about the same; Dell also offers accident coverage, so I don't worry about damage as much.