I am a new Personal License holder as well. Here are some tips of things I was not expecting:
Have a good way to clean the parts. Especially the older cars - lots of gunk can build up. And you need to do a good cleaning of the throttle body after you groove it anyway so no metal shavings go in the cylinders.
I got a variety pack of different size vacuum line caps and T and Y connectors. I am getting some flexible vacuum hoses of different sizes too. This is more for grooving other cars where you don't know exactly what you will need.
Ask questions. Other Gadget-men have been very helpful to bring me up to speed. The more I learn, the more I realize there is still to learn.
Take pictures before, during and after, and post all your mods. I am trying to document my mods in a way to walk someone through the same car. It would be nice for me, and you, if others did this as well. Then I can know what to expect, what extra parts I would need and if there are any special situations. Having that extra knowledge helps build confidence and the customers can pick up on that. It validates you and gives a better business-side delivery of the groove.
I understood the groove and the air flow, but the PCV and vacuum system was new to me, so there was a quick learning curve there, and it sounds to be the same for you. I would suggest learning about what the PCV valve does, and the vacuum system in general. I found it easier to learn about the concept first and then I can understand how each manufacture puts this same principal into their engine design in a slightly different way. Once you get the big picture of the PCV and its effect before and after the groove, then it is much easier to understand. In general, any vac lines that come into the air stream after the groove is bad. Reroute them to a point in the air intake stream before the groove. Some cars are more complex in this vacuum system and some lines go to brake systems - so know what you are moving and some things can not be moved. It is different per vehicle, but the concept is the same. Read through old posts on the forum - there is a lot of good info here.
Explain the effect of the groove out loud to yourself, then to a friend, then to any customers. You learn something the most when you teach it to others. When I started explaining to people what I was going to do to their car and why, and what the result would be, then I began to understand the whole thing much better.
Have Fun!!!
Dan Grieve
South-Central Missouri