Which raspberry pi 4 to buy?

What is the problem?

Is there any point to getting an 8GB version of the raspberry pi 4 to use as an octoprint server? Will a 4GB or 8GB suffice? Would it be better to have more RAM if i ever wanted to stream ?

There's not even really a point in getting a pi 4 at all - it's already overpowered.
The cheapest version (should be 2GB) is more than enough.
This has no effect on your ability to stream.

My rpi 4 4GB only uses 180 MB memory with a load op plugins and the rpi v3 camera connected.
So I'm sure a rpi 3 with 1GB of memory will be more than enough.
( I just had this rpi 4/4 available when starting with Octopi).