How many sets of armor does Erza have? I have been wondering this whole time since I recently started watching Fairy Tail.

How many sets of armor does Erza have and how can she make new ones?
It was never mentioned exactly how many equipment she has, but according to Fairy Tail Wiki:

Erza owns over 100 different types of armor, and over 200
different types of weapons.

A part of this equipment is stored in other dimension and the other part is placed at her room, as mentioned in the section The Knight (name of Erza's requip skill):

This Magic allows the user to store weapons and armors in pocket
dimensions and summon them during battle.
[...]
there is a limit to how much the pocket dimension can store, and as a
result, she leaves some of her armors in her room in Fairy Hills.

And answering your second question, Erza is an user of requip magic, in other words, she can summon weapons and armors during the battles, but she does not create them.
Here or here you can see the list of all weapons and armors that already appeared in the manga/anime.