Some random thoughts, in no particular order...
Are you going to have to buy sails "mail order"? Or, are there some sailmakers near enough to come to your boat?
And then, even if someone does come and do the measurements in person, you need confidence that they will do a proper job and absolutely guarantee their work to fit.
Back in '80, I used to measure boats for a sail maker up in Seattle. I was always nervous about the numbers and checked everything several times. I was using a printed guideline to "fill in the blanks", just like they would use for a boat visit. No problems with my numbers. Economically, it was a sideline for me, in any case, and I was actively in business for only a few years. I was racing OD at the time and selling a line of small boats for a little builder that had lost their local on-water rep. for a while.
Your concerns are well founded, but will also help keep you sharp as you participate in this process. When you do the basics, you can understand and much better communicate with the pro's in person or on the phone.
To pick a sailmaker I am familiar with,
UKSails has a Measurement Form you can d/l.
http://www.uksailmakers.com/Resources/PDF-Librabry.html
Lee Sails has a form on line too.
http://www.leesails.com/quote.php
I imagine that whatever loft you consider has something similar.
For starters, take one of their printed-out forms to your boat and a long cloth tape measure and just start in. After all, no matter who does this, the actual measurements of YOUR boat are the only ones that are useful. Knowing if you have a Standard or Tall rig is ok for getting a "ball park" quote over the phone, but will not (!) replace real numbers from the actual boat.
Most sailmakers that I know will require some photos of the outhaul part of the boom and of the goose neck. If your boat does not have roller furling for the headsail, this is the most economical time to add it, BTW.
Your digital camera is your friend in these here modern times. You can email info and photos and get quotes back in a day, or sooner. :nerd:
Many here have done what you contemplate now. We can offer encouragement, albeit at a safe distance!
Another thought, another E-sailor in your general area "Grizz" has been making some light air sails from kits on his home sewing machine. He sez that they work well, and he really liked the learning process... save some $$, too.
Regards,
Loren in distant PDX