That is the generally approved method for creating cottes/kirtles/medieval era self-supporting gowns. Both I and several sewing friends use this method, although I only use safety pins, I don't bother basting. (You can even see it being done at CTRF if you stop by the Aetas booth when she is doing a kirtle fitting) It is very handy and does give a very good shape. The three problem areas to watch out for though, especially if you are newer to patternmaking, are:
1. Using a cotton (which won't stretch as much) or using a different type of linen(which will stretch more with the body heat) than the rest of the garment is going to be made out of. This can cause problems when transferring from fitting to garment cloth later in the process.
2. Fitting it so that you end up with boobs popping out of the top. Often this is because of the above note. Since the bodice needs to be soooo fitted below the bust in order to support the breasts, you can end up getting more of a fantasy push-up “boob-platter” than a pleasantly uplifted bodice if you aren't careful. The opposite can also occur though, especially as your linen stretches through wear, and stretches, and stretches…
3. They mention to be careful in cutting out the armscye in the front. I can't stress that enough. Even for more experienced sewers, that is a finicky area, and the way that this is fit on the body makes it very prone to making that incorrectly. That is one of the major reasons that I always recommend using a mock-up material for the fitting, then transferring the pattern to paper so that you can see what it will look like with out the wrinkles or stretching caused by the fitted fabric. Then you can make sure that it really looks the way it should before you cut out your expensive cloth.
The other reason is that way you have a pattern that you can use over and over without having to fit something again. Saves so much time!
Also, as a side note in relation to our period. This is a fantastic method to use with front lacing garments. However, if you are relying on hooks and eyes/bars to close the front of your bodice; it will put too much stress on them and you will end up with gaps, bent metal, or slumping boobs. (Well, unless you have less than a B cup or you bone the front edges of the bodice)
Ummm, that was long, and I am going back to sewing 18th century dresses like I should be doing at work…Is it a good time to warn you now that I can go on for a really long time about historic clothing?