I've been thinking some more about getting a temperer
vs. tempering by hand (with or without a marble slab).
Any comments on these thoughts?

1. A tempering machine is mostly useful for holding
chocolate in a tempered, liquid state suitable for
dipping. If you're just blending chocolate and casting
into a mold, you actually want to dwell for the minimum
amount of time in the molten state. A tempering
machine automates the temperature control and
keeps the batch in temper by constant stirring,
but it does not prepare the seed for you. Unless
you need hold chocolate in temper for dipping,
a tempering machine is just an expensive source
of heat (albeit with good temperature control).

2. A marble slab is used for some manual methods,
because the methods assume a) you've got one for
other confectionery work, and b) you'll be using the
tempered chocolate for dipping, rolling, etc. for
which having it on a marble surface is the traditional
way of laying it out in preparation for other work,
and c) the seed is prepared by spreading out some
liquid chocolate on the slab to solidify. A doesn't
apply to me, because I don't already have a
marble slab. B doesn't apply, because I'll be casting
into molds. C is avoidable by preparing the seed
using a different method (like grating up a chocolate
bar). So, I think I don't need or want a marble
slab. A Kitchen Aid mixer might useful for blending
the melted chocolate(s) and adding flavors, and then
for adding the seed, but I don't need a temperer
or a marble slab.

I'm thinking the best chocolate melter would be to
find a precision temperature controller (probably
an OEM unit) and using it to control a crockpot
slow cooker. I can't use the existing temperature
controller, because it doesn't go low enough and
has too much hysteresis (gap between turn-on
and turn-off temperatures). And I should go to
a potter to make a replacement ceramic crock
for the crockpot. It would have the same outer
dimensions, but the walls would be at least three
inches thick to increase its thermal mass. The
inner cavity should be the size of whatever tray
I use to hold the chocolate. It can be pressed
into the clay before firing, to ensure good fit.

If I had two of these modified crockpots, I could
have two stable temperature environments,
one for melting and another at the tempering
temperature.