Hi. Welcome to the site.
Locksmithing as a hobby or career is greatly rewarding. I still get a kick when I struggled with a challenge and "it" gets solved. So enjoy it.
It depends on how long you have been in the trade but specializing in auto locksmithing can be quite luctrative. I have a buddy that does this and he has the knowhow and tools to do virtually any car.
My best advice is to go to the scrap yard and befriend someone important. Then you can start teaching yourself how to open cars, Stripping locks from doors and the door mechanism etc.
Also get the word out to car dealerships and auto repair shops that you specialize in cars. Secondhand car dealerships and auction places are always loosing keys.
Learn impressioning. Helps allot.. There's a ton of tools that can be bought, lots quite usefull. Get advice always. This forum is a definite asset for this.
79commando wrote
Finnaly all you need is to spend a few grand on advertising
This is a must if you're serious about this career. Don't underestimate advertising.
Good luck with your choice and this is do-able