A couple of things spring to mind in response to your questions.
- Bezel fitting. Shouldn't be too tight. It's the tapping over
and then subsequent burnishing of the bezel that will give you that
smooth look, not how tight the bezel is. Rule of thumb is that once
the bezel wall is soldered together, if you have it sitting on a flat
surface, the stone should "slip" in with absolutely no pressure or
pushing on your part. The space around the stone should be visible,
small, but even all the way around -- that's the key for it not
looking sloppy. If it's too tight, try the suggestions published
here recently -- rolling with a round dapping punch to stretch it
very slightly on each side (roll the same number of times and with
the same pressure on each side so that it stays in proportion).
Also, if you have square corners or sharp angles on your irregular
shape, you will need to allow a slight bit more space so that the
bezel has room to "turn" the corner. One thing that will help here
is to use your sawblade and create a very small cut at the corner
that goes no further down than the point where your bezel stops
turning over the stone. This creates a small mitre joint, so the
metal won't crimp at the corner. In essence, one side of the bezel
metal will lay over the other side at the area of overlap, but once
burnished, you won't see it.
- Avoid step bezel wire. (My personal opinion follows - I am sure
there will be those who disagree.) Step bezel wire will frequently
distort and is generally a pain in the butt to work with. A better
solution that avoid the problem you're describing is to use an
underbezel constructed of a small-gauge square wire. You can solder
in the underbezel if you want to, turning it into the floor in an
open-backed setting, or you can simply drop it in under the stone in
a close-backed setting (rolling the bezel locks in both the stone and
the underbezel). In either case, the underbezel should be shaped as
closely as possible to the inside contour of the bezel wall, fitting
snugly under the stone on all sides.
That's my $.02 for the night. I hope it helps.