Hi,
I'm not sure what you mean by #4 but in general, I would say the 2 simplest options would be Google App Engine (GAE) or Google Compute Engine (GCE).
1. I would start with GAE (standard environment unless you have some unique/complicated stuff) and then migrate to GCE if I need to later. I'm recommending GAE because you don't have to worry about scaling your infrastructure to meet your demands. You just write your code, deploy it and Google takes care of scaling up/down to meet changes in your traffic. Google also gives you free SSL and you can use your
custom domain on GAE.
2. Development is done on your local machine and you deploy to GAE by either using the gcloud command line interface (gcloud CLI) or a 3rd party GUI (I have one -
https://nocommandline.com). Since the code is local, you take care of versioning and/or sharing amongst different people anyway you like. If you want different people to be able to deploy, you can grant them access (
deployment role) to be able to deploy or make them co-owners of the product
GAE (standard) will not work if you need any of - streaming, instant messaging (like PubSub). For those, you'll need to use GCE or maybe GAE Flexible (you'll have to confirm the information about GAE Flexible)
..... NoCommandLine ......