al.b,
I use Caffenol as my primary print developer. It's quirky, but if you are patient you can really get some wonderful results. I tend to mix it about double strength for printing, and give the prints a good rinse in the sink before hitting the stop and fixer baths just to keep the coffee stain from contaminating all my trays. As for capacity, you can generally judge it by eye, but I think I get about half the number of prints as I would out of traditional developers.
BTW, The washing soda is available here in Ontario. I live in Leamington, near the gates of Point Pelee, and have no trouble buying it. I use Arm & Hammer "So Clean Super Washing Soda", which works well in Caffenol and also as a bleach for cyanotypes as well. A box of washing soda should last you several years.
Cheers,
Tom