I have used a 2000 gm capacity scale (cost about $99 nine years ago -- they
are cheaper now) with a resolution of 1 gram.  I have rarely, if ever, felt
the need to use a higher capacity scale, since I can fill up a 16 oz mixing
cup with epoxy and still use the scale.

2000 grams is 4.4 pounds of epoxy!!!!  Of course that's usually plenty.

I am reluctant to use batches smaller than 20 grams due to the coarse
resolution.  I would prefer a 0.1 gram resolution -- then I could mix smaller
batches.  I think that any capacity from 500-1000 grams would be perfectly
fine.

How much to mix?  I've discovered that I need 1/2 gram per square inch of
glass for small layups, and 1/3 gram per square inch for bigger layups.  
Estimate the number of square inches, multiply by the number of plies, and
then divide that number by two or three.  This is the weight of resin only --
add the hardener in the appropriate quantity.  Use that much resin and add
hardener to taste.  (Well, not really "to taste"...)  You can print out a
graph and post in on the wall to save trying to find your sticky calculator
-- or you can put your calculator in a baggie like John Kleber does.  (That
was a *great* idea, John!)

This amount of epoxy is not what goes on the plane.  I always have a little
left over for painting a thin layer on the prepared surface, wetting out peel
ply, a little leftover for trimming, etc.

I use large 4 mil plastic bags to plan my layups.  I buy these 24 x 14 inch
bags in quantities of several hundred.  (They are pretty cheap and much
easier to deal with than segments of huge plastic dropcloths.)  I draw the
desired layup shape on the outside of the bag with a fat sharpie marker.  I
scribble on the outside of the bag in the middle of the layup so that I can
see the piece of plastic and make sure I peel it off of the plane.  I spread
epoxy on the plastic, add a layer of BID, and repeat as needed.  (I used to
close up the bag and use a roller to squeeze out extra epoxy but that didn't
work too well.  Now I do that with the squeegee.  So I really only need one
side of the bag but the other side is a handy place to drop squeegees, mixing
sticks, drippy cups, etc to keep my workbench cleaner.)  Then I take the
pizza roller and cut out the layup.

This is why you need more epoxy for small layups than big ones.  If you have
an inch or two of wet-out epoxy all around, then there's more waste on a
small layup than a big one...

The plastic "carrier plate" keeps the BID sandwich from stretching as you
position it on the plane.  Peel it off when you need to -- you can keep it on
longer on flat layups but you have to peel it off earlier on those
complicated corner layups.

Sorry if this is too basic for you experienced guys but the newbies might
find it interesting.  Everyone has their own special "tricks" and I'm not
proud -- I steal the good ideas from anyone!

- Rob Wolf