I am working on a typeface and have started with a somewhat thicker style that would usually be called "Bold". Can I make it "Regular" or is it unusual for a certain thickness?
Here is the thing, the styles are a way for us to crate hierarchy and differentiate between different "looks" of the same font. Bold is a good way to use the same font but highlight a part of the text, also italic.
You obviously wouldn't call something "light" if it's thicker than the bold. That being said, Regular is a bit different, since as it's name says it is the the default, most common or "regular" appearance of the font, so it doesn't matter if it's relatively bold or light, as long as you categorise the other weights accordingly. Also you can describe this as a "thicker" font.
Go right ahead. You can call your weights whatever you like, within reason. If the name "bold" bothers you, you can call your base weight "light" or "thin" and then move upward through Book, Regular, and Medium before reaching the big scary Bold. Helvetica Neue has 25 through 105, I think, to delineate weights, so there's plenty of range.