Fran, Allan et al- Now you guys are going to make my cup of tea siting next o the keyboard get cold again. Tools......
Everyone has their own tool kit within certain limits for any given job. I tell my students this overly simple "secret" to carving: Look at the shape you want to create, find a tool with that shape, push it through the wood, and it will leave that shape.
We all have tools that we prop the window open with, and for this purpose I use spoon gouges. Not that they are not useful from time to time, such as the hollows in the lobes within the rosette, for instance, but I have managed to get along without them for the most part. If you're making spoons, well that's another story. My theory is really that whatever works for you is what you should use. "Economy of cuts" is really what your mantra should be. The fewer tools you use, the faster you'll carve.
Parting tools I use to lay out the fillets ( see the FWW article I wrote some years back) and do long runs such as the layout of acanthus leaves, as well as the dreaded wavy line around the perimeter of some shells. A parting( or V) tool ground back will enable you to run across the grain as well as along the diagonal fillets going in either direction- this last move due to some interesting geometry of the grind that's not important to explain here.
My second favorite tool for the same reasons is an 11-7 ground back in the same manner. This is universally useful in doing the hollow lobes of the shell. My elapsed time to carve a shell, and I reluctantly include this to emphasize the usefulness of a customized tool kit in these projects, is about 5 hrs. Economy of cuts.
I wouldn't carve a shell in cherry unless I had to due to hardness and grain, as well as tradition. Walnut would be OK, but you'll be using a mallet more, as you'd have to in cherry also.
I think the desk I made for the sect'y base was 41" wide. As Fran said, they vary. I have plans on my web site if you really want to make one of these things. The Brown model was too tall to look good. See others such as those at the Met, MFA Boston and Yale for better proportions. Don't try to squash the pediment to fit it into a smaller space, this will cause a lot of anguish and the results will be terrible- it's really tricky to change this element and still get good proportions. I had a student who was a rocket scientist and an architect and he couldn't make it look right. If you want to shorten the piece, take it out of the door height.-Al