Is serverpod really for me?

[mjablecnik]

Hello, I want to create backend service with REST API for my personal project where will be SurrealDB as a database, Flutter used for mobile apps (in future) and plasmic.app for web pages.
I want to obtain my data for Flutter and web sites.
I think that REST API is sufficient but I see that serverpod generate client for Flutter but I didn't find if is really simple to create REST API also for web pages.

I was considering about serverpod, shelf and serinus.
Serverpod have very bright future, great development progress and growing up community but I don't want to use Postgres DB so ORM from serverpod is useless for me and I don't know how much tight is model generator with database. (I will use Models, but not DB what serverpod prefer)
Shelf is very simple and serinus is very pretty but it is not so far with features as serverpod..

My questions are:

1. Is serverpod also for non-Flutter projects where I want to create only REST API for already existing services?
2. Is serverpod also for projects where I want to use some other DB then Postgres?
3. When serverpod generate own client. So client communication is via REST API or is it some type of gRPC or something else?
4. I looked out differences between Serverpod and Serverpod Mini and my last question is: Why it is not more modular?
   For example: I want to use file uploads or Task scheduling which Serverpod is missing but I don't need really every functions of whole Serverpod (for example: ORM, Relic web server, or redis caching)

Maybe I will use Serinus which is more simple and modular then serverpod but I want to see also your opinions..