re: testing — I’ve seen SAM Local for quick iteration on Lambda and API GW work well, combined with remote cloud services for (E.g.) database.

A Cloud Guru have been fairly vocal about using the AWS / Firebase combo. The key to me is isolation and automation — give every one enough of their own environment that they’re not getting under each other’s feet, and automate the heck out of managing those environments.

Which leads into your last point … John and I are big proponents of multiple environments, e.g. AWS sub accounts. Without reference to much else I’d have 1 environment / dev / task, and treat them as ephemeral as possible. AWS don’t make this completely easy (no automated deletion of sub accounts, chalk that up for the #AWSWishList), but you can create them and monitor them in an automated fashion.