I would guess the max would be the maximum size of nvram. Each username/password is stored in the config file and the config file can only be as big as NVRAM. In most of my clients, after about 5 users they want RADIUS auth setup. Makes everything a lot easier.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...