Massive portupgrade without being interrupted by configuration screens?

[b. f.]

 > Are there any adverse side effects if I use portupgrade some of the
> time, and postmaster other times?

Probably not, if you keep your portupgrade portsdb and pkgdb
up-to-date, and you are not doing anything special with pkgtools.conf,
portmaster.rc, or environment variables.  But you don't really need
both, or, for that matter, either of them.  For instance, you could
just use the base system utilities and do something like:

pkg_version -qol '<' | cut -f 1 -d ' ' | xargs -o -t -I % make -C
/usr/ports/% config-recursive

(For a speed-up, if you are sure your INDEX is synchronized with the
rest of your ports tree, you could add the -I flag to the above
pkg_version call.)

> Reason for wanting to do all "make config"s beforehand is not only
> efficiency and ability to run unattended, but the ability to recover
> from a typo at the config dialog interface, which can be confusing,
> on when to press spacebar, tab, enter, up- and down-arrows.

This is what the portupgrade -C/-c flags are for.  if you want to do
the configuration as a completely separate step from the updating, for
whatever reason, you could run 'portupgrade -can', for example.

b.