Mick,
When it comes to machine tools I guess the question is how much money do you have? He will need a lathe that has 36"-40" between centers. This can be new or used. If you buy used, be sure to get someone to go with you who knows machine tools. A Bridgeport type mill is the best if you can afford it, but good work can be done with the bench type sold by Enco and Harbor Frieght for approx. $1200. Don't forget all the extras that are needed such as milling vise, mills, cutters etc. The cost can really add up fast.
Other things include a drill press, 12" disk sander, oxy-acd. torch set, bench grinder, electric drill.
I started out with a drill press,bench grinder,torch set,6" disk sander (save your money and get a 12", these can be had for about $100. from Harbor Frieght) and a good selection of hand tools.
I try to buy the tools on an as needed basis and let the job pay for them. I bought a small 10" lathe from harbor Frieght for $350.00. I cannot thread and chamber rifle barrels with it but it does good work on handgun barrels and for making small parts and tools. I am close to buying a full size lathe, but have not decided which one I will get. Then comes the mill. You can do alot of work without the major machine tools when first getting started and farm out the work that you cannot do. Not as much profit, but you don't have to send the customer away. Finding the right place to open your shop and getting the word out that you are in business are the hardest part. I live in a small community in Idaho with several other small communities around me. It does not have a large base of people, which is a handicap, however, just about everyone who lives here has numorous firearms. The next closest gunsmith is an hour away. I work out of a shop in my home that has it's own enterance. This greatly saves on overhead. I advertise in my local paper with a small weekly ad, put up fliers everyplace that I can and pass out business cards to everyone that I meet. The best advertising is word of mouth as long as the customer is satisfied that you will do a good job for them. It was really slow the first 8 months, but has been picking up greatly every since, as the word of my work got out. I charge reasonable prices (not cheap) and always try to do a little something extra for every customer when possible. I figure about another year at least before I will have enough business to go full time.
I hope that helps. Your son is about to get into the part of the course where he repairs firearms. When I got to that section I told the head instructor that I wanted every tough job that they had. Some students wanted only the easy ones. If you are good enough at repair, and prove yourself to the instructors they will give you these jobs. If you do a good job on the hard ones you will really earn the good grades and will learn much. You can pretty much learn as much or as little as you want to there. Pass that onto your son and if he applies himself he will get the most from his education. Also tell him to get as much referance material as possible. You will spend a pretty penney getting a good library, but it is well worth it.
Best Wishes, John K