I generally prefer convex grinds for outdoor work. They tend to whittle much better than hollow grinds, and provide more strength and control over the cuts. If it's wood you'll be cutting, convex is a great way to go. Convex grinds are also good for cutting meat and other natural materials.
Convex grinds are also easier to sharpen in the field than hollow grinds, IMHO. No SharpMaker required to hold that perfect angle. For more convex grind info, try this link.
Convex Grinds
I do love hollow grinds, but prefer them for more urban utility work. A hollow grind will sometimes allow a blade to pass through a certain material with less resistance, just because the blade is generally thinner. Hollow ground knives are also lighter in weight than convex ground knives, as there is less steel in the hollowed out blade.
5/32" sounds great for an outdoor knife. For this type of knife, I wouldn't want to go any thicker. At this size, it won't be some sort of big chopper or anything. It just has to slice and whittle a bit. Anywhere between 1/8" and 5/32" should do fine. If you plan on cleaning many fish, I might lean towards the 1/8".
As far as the handle length goes, that's mostly a matter of your hand size. I love the fit of both of my Doziers, and I have a medium sized hand. A very large hand might require a bigger handle than I normally use. Just make sure that you properly communicate your hand size. Nothing sucks more than getting a knife with a handle that doesn't fit your hand. It's dangerous too.
4 1/2" sounds good for an outoor knife. It's that nice middle-of-the-road length. Very versatile.
It is worth chatting with Hoodoo about his convex ground PKG. Hoodoo knows his knives well. If he loves his PGK as much as he says, it could be perfect for your needs. It's VERY close to your specs.