I'd say dipper and Old Guard Dog have covered the realities. I'm a retired custom gunmaker and machinist of over 4 decades. Follow your dream but keep the realities in mind. If you are passionate about it (as most custom gunmakers usually are) you will understand the need for patience. Customers operate on 'trust' and 'faith' that you will produce what they want. On the matter of gunsmithing... remember that they are putting their treasure in your hands. Each and every one of them will be concerned about how you take care of 'baby'.
One other little item every gunsmith should know. There is very little, if any, money to be made in gunsmithing the average .22lr rifle. When you figure the cost involved... you can just go out and purchase a new rifle for less. If it's an heirloom or a treasured longtime friend of the field... then the customer just might be willing to pay the price. If you intend to be a one-man-shop, you'll have to look at either high grade custom or volume. Sometimes folks specialize... i.e. trigger jobs, building 1911s, etc.
Above all... learn to use the hand tools (especially files). Power is nice but it can get you in trouble if you are too dependent on it. Striking barrels, inletting, inlays, stock refinishing all can be done with hand tools and give you a closer feel as to what you should be doing. Power is OK in its way (I have a complete precision machine shop) and I use the power for specific operations. However, even my chamber jobs are finished by hand and the bolts just barely close on the 'go gauge'. My tolerances for some operations runs about .0005" and that does require power.
Throw yourself into the apprentice job: make some fine firearms and put out some quality gunsmithing. Remember that folks talk and every job is unique to that customer. It might be your 100th trigger job... but it may just be the customer's first.