Advice on starting my own men's underwear line?

I have been sitting on this idea for about 2 years..being a designer underwear enthusiast, I have a brand name created that is still unregistered for trademark as well as many photo-shopped designs, collections (along with names of said collections), etc. I am looking to branch out in the online world first as well as a few contacts in local boutiques that sell men's designer underwear. Any advice on startup costs and skill level it takes to manufacture this? Any and all information would be greatly appreciated, thank you!