In terms of paint, I use mostly Testors and Citadel. For sculpting, I use Aves Apoxie Sculpt & Fixit Sculpt, Super Sculpey, and Kneadatite's Green Stuff and Brown Stuff.
You can buy Aves products here: Aves Studio
You can buy all kinds of Sculpey here: Sculpey
That depends on the job. Each figure is priced based on the details and parts involved. They are expensive though... the average is a few hundred dollars. Email me and we'll figure out a price.
I always ship via USPS Priority Mail with delivery confirmation and insurance.
That really depends on how good business is, but it's pretty common for around 5 projects to be on the work bench at a time. Working on multiple figures keeps me from getting burnt out and helps to prevent the customizer's version of writer's block.
There are a few exceptions but, generally I do not.