In this area I outline a few details along with some thoughts for your consideration.
I use a standard "X" brace pattern for my steel string guitars. This is a proven design and there are some long-lived guitars that used this pattern so I know it can stand the test of time. Also, being perhaps the most common, some pick-ups are designed with this scheme in mind so it's good to know that you are not likely to be limited in choice of pick-ups due to the location of braces.
With respect to scalloping the braces, I do gently scallop mine as I carve them. This is the approach I take to reaching what I feel will be the optimal size for the brace. I do not believe in deeply scalloped braces as I feel a long brace should still act as a single unit across the sound board i.e. there should not be "weak" spots in the brace.
Binding and purfling can really make a guitar in terms of appearance. The vast majority of guitars available in stores use a plastic binding because it is relatively easy to install (it doesn't have to be pre-bent to shape). On almost all of my guitars I use wood for the bindings because it looks classy and that is what most people want on a hand-crafted instrument. I am not opposed to plastic (ivoroid) as in my view it can look good and it is quite functional - it doesn't dent as easily as wood. The guitar to the left has ivoroid bindings with a herringbone purfling. Binding can also look good around the fret board and guitar head.. A very "clean" look is an ebony fret board bound with ebony.
The most popular areas for inlays are the fret board and guitar head. The "Hawley" logo inlayed in mother of pearl is a standard item on my guitars. There are many commercially available inlay sets from which to choose or, a custom inlay such as shown to the left can also be created.
Running a stripe up the back of a guitar is common and can look good. I have found however, that just as often the wood itself is so beautiful that interupting the grain pattern with a stripe would take away rather than add. Sapwood can create a natural stripe.
I am happy to install a pick-up of your choice. This can be done after the guitar is completed unless it includes something to be mounted through the side of the guitar. In this case it would be better to add support wood to the inside of the side during construction. When making a decision about electronics, my advice would be to keep in mind that they are getting better all the time and change frequently. Therefore, in my view, it is best to choose something that can be replaced easily without extra holes to contend with i.e. avoid systems with though the side mountings.
The guitar to the left shows the LR Baggs "Anthem" controls mounted with two-way tape beside the sound hole. I am very impressed with this system.
On non-cutaway guitars I use a standard heel shape. On cutaway guitars I like heels that line up with the edges of the cutaway side. To me the shape flows better than the corner that results from having a standard heel on a cutaway body.
I don't like heels that are too large as they look clunky.
I offer two choices in finish, one very traditional and the other very modern. These are: French polished shellac and ultraviolet light cured polyester. Some believe that a French polish is the most acoustically transparent finish and, for this reason, it is often the choice of classical guitarists. It is, however, relatively delicate and can be worn off easily. Polyester finishes are very durable and, if done properly, can also be quite thin and acoustically sound. It has become the finish of choice for many large guitar companies. Not too many individual builders offer it as there is a significant cost to get set up. It is the finish I recommend for most guitars (classical included).
Purfling between the binding and the sides of a guitar can look quite good - especially if mitres are made at corners such as shown in the guitar to the left.
A veneer on the back of the guitar head can be quite dramatic. The one shown to the left is in Brazilian rosewood. Solid colour veneers, such as black ebony or red bloodwood can also really show off the tuning machines nicely. A veneer also covers the line resulting from the scarf joint that joins the head to the neck.