One question about the verbiage on the website for the "Team Starter" plan: It says "_Up to 20 project stacks_." Does that mean you're allowed 20 stacks per project, with unlimited projects? Or is it 20 stacks, distributed however you want among n projects? For example, 5 projects each with 4 stacks.

I believe it's the latter

It is the latter, though it’s soft-enforced; we don’t block creating a 21st stack, we just message in the Console about being over the limit.

I assume it triggers a Sales Drone Raid on your mailbox.