If the chamber has been CNC'd, I like to have the dome clearanced MIN .020" at any point in the whole profile of the chamber, at ZERO piston to head clearance.
If the chambers are not all exactly the same, shaped by hand, then it's just a more difficult, time consuming job.
As for doing the actual shaping, I like to put the piston in a soft vise, and use a variety of carbide burrs, and, or, a variety of abraisive tootsie rolls. You need something to hold the piston tight, so you can concentrate on what you're doing. When I'm done shaping I like to use emery cloth over all the edges and top and polish/smooth them all out.
For Valve Reliefs, I assume you're talking the brows, I like a generous radius on the intake brow. The exhaust brow is not as critical in terms of the radius.