Application server, but the line can be very thin.
I’d say obey.
Newbies, as NS7.
I’d go with the same partition, if you have enough space: it’s easier to maintain.
Still, this is a choice of the sysadmin.
Take also a look to https://nethserver.github.io/ns8-core/best_pratices/#adding-more-disk-space (may this can help also @Axel)