You have already done a lot of research and thinking on the subject.
Two thoughts come to my mind.
With any business, some actually business management knowledge is vital. Do consider taking some small business managment courses.
And, you will need to keep beans on the table. Starting part-time while holding a job might be the way to go. Starting from zero is like climbing a mountain without ropes. Especially gunsmithing. Customers need to learn about you and build confidence. Good luck.