This is a fantastic break-down of the system that I'm definitely going to be referencing for some time. Thanks for putting so much work into this! That said, I do have one question so far:
Since the cost of items in NuYen doesn't increase post-gen, many purchases can safely be postponed until after creation. That said though, the rules for buying hits on Availability are pretty harsh (a contact with Connection:6, Loyalty: 6 AND Black Market Pipeline can only find Avail: 5 or lower items for you without markup, and a face would need 48d6  to acquire Avail:12 gear), so it may behoove you to acquire difficult-to-come-by items now (This is what makes Restricted Gear so good).
I think you missed a step in your Availability calculations. My understanding, and how it's been ruled at my shop and the conventions I've attended, is that Availability (at least per Missions) is calculated through bought hits (for both purchaser and item as it's an opposed test), which makes it easy to eyeball what can be afforded. The Contact you listed would have 5 bought hits, as you listed, so they could purchase anything that gets 5 bought hits or less (baseline 20, arguably up to 23 depending on how you rule with rounding up vs. down). So, this being the case, a starting Contact of Connection 5, Loyalty 2 would be able to access Availability 12 gear (5 x 2 + 2).