I own an inside bevel chisel (incannel I believe), but have no use for it. Curved outside gouges are great for removing material from the bottom of inlets and are sometimes useful for the edge of inlets, but curved inlets can be well generated with straight chisels. The straight chisels for this however must be very narrow, like .060" or less, which usually means hand made, but straight chisels are very easy to make. It also is slow to generate a curve with a very narrow chisel, and (I think) a lack of patience is one of the biggest obstacles to nice work.
It is nice to have two small gouges, one with a small radius and one that is much "flatter" to smooth the botton of an inlet before flattening with a "scraper". which is a straight chisel held perpendicular to the work and dragged across it.
As for sets, after you have a six piece general carving set, buy chisels and gouges etc. one by one as the work demands them.