Yes, it does no harm to switch to ROLLFORWARD mode in mid-stream, it just
works.

It does fire an extra DB backup; or maybe that's when you switch BACK from
ROLLFORWARD to NORMAL, I forget.

The amount of log space you need depends on the amount of activity rather
than the DB size, so it's hard to say whether 2 GB is enough log space or
not.  You should be OK if you have a trigger set, just keep an eye on the
log utilization for a few days.