plywood dome

Since access isn't an issue I'd use either a bullnose for roughing and finishing or a regular end mill to rough the entire sheet and a standard ball nose to finish the entire sheet. Tapered ballnoses are for 5-axis, when there are access issues, or for high detail topographical carvings.

A proper two-step roughing-finishing method would probably cut down a significant amount of machine time and drastically reduce sanding because you'd be using the ballnose (or the radius of the bullnose) how it's intended to be used. You could also, if you set it up right, start pulling finished parts off of the machine while it's still running, allowing you to finish sand during downtime.

Alternatively, you set up a pallet system, drill holes in the back of the plywood, screw into them through an aluminum pallet, and then machine (still rough/finish passes) them from the front. Once you take them off, you have the screw hole to allow for a quick sanding mandrel to screw in so you can hold it well away from your hand.

 

Thinking about the pallet a little more, all you really need is a sheet of countersunk holes; you can then just screw into every single hole with a short wood screw, and clamp the aluminum plate to your machine. You'd also probe your G54 coords off the aluminum because you want to center the domes around each of the holes, not arbitrarily on the plywood sheet. You could probably get away with 1/4" aluminum for such a light duty purpose, though I'd still go 1/2"-5/8" just so you could use less clamping and still maintain rigidity in the center of the sheet. Or just cut the plywood up and do multiple smaller pallets, so you can load one and unload one while one's machining (which is of course the intended purpose of palletization of production).

Your first run on any given pallet would eat aluminum, wherever your ballnose goes down far enough to contour the very edge of the dome- since you're machining with the side, the tip would be inside the aluminum. You could do a dry finishing run at reduced feeds and speeds, maybe with a little WD40 coolant, without the plywood in the machine, to prep your pallets, if you wanted. That way you don't have to worry about crashes or burning up tools later (the tip of the ballnose has effectively zero tooth and zero surface footage whilst still being forced through the material at full feedrate, remember) when you're running at wood-grade feeds and speeds.

I'd do 1/4" for the higher surface footage and larger chipload per tooth, but check that against accepted speeds and feeds figures for baltic birch ply- I don't machine (or rout) much wood, so I don't know if that might put it in danger of burning. Seems unlikely, but I lack the practical experience to make that call.