Hi, tks for the hints. After read the comments received at this moment to me the best options are 1 or 2 described by you; I'll have to think which one would be better..
Regarding ports 80/443 for each NAS I plan to setup a NPM on each NAS using mcvlan to avoid Synology DSM conflict because Synology DSM use internally ports 80/443. The NPM reverse proxy on each NAS will manage containers installed on each NAS.
By the way, I'm very interested to install NPM container on the RB5009 but I read this post: Horrible container performance from 7.14 up to 7.15rc2