Ahh, depends on what you're doing. Thick and pasty like peanut butter/putty.
You still want it to be able to penetrate whatever join you're working on. It does seem to cut down the amount of working time you have (seems to set faster) in my experience.
IF you were using this for strength (which you are NOT), I'd use milled fibreglass.
Over all, it's difficult to say how much of each. In a way, you'll know when it's just right--it's workable but not as "drippy" as straight epoxy.
Not what you want to hear I'm sure.
Quantity to buy: as small a container as possible. It will last you a long time (as does the milled fibreglass).
You will want phenolic (brown) balloons, not glass. Most boating supply stores stock them.
http://www.compositescanada.com/prod...?idProduct=252 (the pic shows white but they are actually chocolate brown in colour)