Yes. dch -r is the conventional way to do that (and change the
timestamp at the same time), but you can just edit it. The idea is
that you leave it as 'UNRELEASED' until you really have stopped
fiddling and are ready to upload. Some tools take note of this field
to stop you accidentally uploading before you are ready. (I don't
personally find this useful, but that's why it's there).
No. Someone will have to do the work of making any adjustments needed
to build in stable and doing an upload to -backports. That can't be
done until after it has been accepted into the archive (which can take
a while (days to months) after initial upload).
https://wiki.debian.org/BuildingFormalBackports
https://wiki.debian.org/Backports