Thank you for all your helps!

What I recommend is a Doepfer A100 Basic System.

I think I will start off with some Doepfer modules to get some basic learning and ideas. I will also have to learn more about vcas and utilities to help building up this system through time.
For more deeper learning, I will definitely get a Maths for sure.
What are your thoughts about the Beatstep Pro? Is it a good sequencer to control my modular system since I dont want to use the computer to control the system?

Or you could queue up and get one of Uli's ARP 2600 clones.

Sure that the ARP 2600 is a sexy synth. Do you refer to use it as a standalone synth or to interacting with your modular system?