For question 1 it very much depends on your arms. If you have fuller arms you may want to go with a larger size armhole. Otherwise start with the standard size and see how it goes with the muslin.
Regarding #2, I’m not a big believer in the body map concept because it’s not nearly as simple as the authors of the book try to make it. Each pattern will be different and will include a different amount of ease, etc., so even if you make a base pattern fit perfectly it won’t be directly applicable to most other patterns. In theory it’s a great idea, but I know people who have taken classes for this and it hasn’t worked out nearly as well as it sounds. The Bistro Dress would be a good pattern to use, but use it for fit practice and recognize that the changes you make won’t be universal to all patterns. Does that make sense?