What if I delete submissions after they are submitted, are they still counted?

The free subscription says 100 submissions- if I plan to use only 1 form, once 100 users fill it out in a month, that is it for my usage? What if I delete submissions after they are submitted, are they still counted?

That is correct, 100 submissions are given to free users, regardless the number of forms. Deleting submissions does not reset the counter.