Is it possible to have multiple low to mid-level characters at the same time? Whenever I have a low to mid-level character and create a new character, my old character's saves are deleted. Is it possible for me to have both characters at the same time?

As long as you don't just use quicksaves and autosaves then yes. You can have multiple characters by using the save menu and making new saves.

Don't just rely on quick and auto-saves. I have about 4 characters right now.