Hi Phil,
Congratulation on finding that job!
These are important concerns that all beginning watchmakers should and usually do have.
If the following conditions are already in place then you’ve got the perfect opportunity.
I’m going to answer these questions indirectly. What I’m about to write is meant to protect you and in no way to discourage you from moving forward towards a watchmaking career.
The first thing I would stress here if you haven’t already done so is; you MUST tell your employer exactly what you’ve mentioned here about your experience. Having successfully completed 5 watches is a good start but still places you at the beginners level. It’s very important that your employer understands this before HE takes on the risk of having you repair all pocket watches that come in. From what you wrote it’s not clear whether the shop already takes in mechanical watches and whether or not your boss has experience with mechanical watches and can cover for you when problems beyond your proficiency level arise or if he will be depending entirely on you to take on the task. You did mention that it’s an old shop so if he’s the original owner then mechanical watch repair is most likely already a part of the business. Again it’s not too clear to me.
In most cases people starting out who find employment in the field do so with people who can offer support when problems occur. If this isn’t the case and help isn’t available when needed then this endeavor is something you should approach with caution and possibly re-consider.
If all of the above is covered ie: your boss is experienced and can cover for you when needed and he fully understands your experience level then he is well aware of your concerns and has already factored them into the offer made to you.
Also you mentioned that he wants you to clean all pocket watches which may mean that he does the actual repairs if necessary. If that’s the case then he’s most likely an experienced watchmaker and needs you to help him with his repairs so absolutely GO FOR IT!
Most people doing pocket watch repair for the public start out very slowly. An example would be some of the clocksmiths up here on the forum who are now also moving into watch repair. They generally are very careful about telling their prospective customer that they are just starting out with pocket watches, leaving the decision to the customer whether or not to go on with the repair. They also let the customer know if it’s beyond their level of expertise and that it would be best to either find someone else with more experience or to wait a while until they have acquired more experience.
Again I don’t want to discourage you from learning and earning but I certainly don’t want to see you get into trouble or be in a high pressure situation due to a lack of understanding between you and your boss and from your post it isn’t clear to me what the situation is.
If he’s experienced and the above conditions are already covered then you can relax, knowing that he already is aware of your concerns and expects parts to go flying or occasional problems to come up.
I hope these conditions are already in place as this is the perfect dreamed for opportunity! If so then CONGRATULATIONS!
Let us know Phil,
Bob
. Of coarse, at any job there is the fear of messing up and it is my opinion that having some of that fear is good (at least for me) because it can drive you towards being better at what you do. But, as we all know, things happen and we have to learn our lessons 🙄 and correct any mistakes remembering that it is not the end of the world. instead of saying “I hope I dont ruin something” try saying to yourself “I will do the best job I can for this customer” stay calm, take your time, concentrate, stop if your not sure, keep learning, ask lots of questions and have fun 
. So, in the end, yes, I do get that fear on everything I work on (especially something that parts are not available) but I try and harness that fear by concentrating and thinking positive. I recently started to work on the pocket watch and have a few of my own to start with, 1st one I took apart, the collet on the hairspring broke 😯 at the point it was pinned, I didnt like the idea of that happening 🙄 . Now I guess the only way to think about it for me is that I am going to learn how to solve that issue, now if that would never happen how would I ever learn to do it?????? 
