after I did some more reading on several filtersystem I discovered that 2 out of 3 lenses have a great problem with filters. The lens barrel rotates and so the complete filter would rotate too and drop on the ground.
The second problem is that I need to use 4x4/4x6 filters instead of P size filter. I can mount the P size filter, but I can see the corner of the filters on the pictures.

This means, I tripple the money which I need to spend. At least I found out that a circular polarizer should be the highest priority and also the most expensive.

and later if money permits:

- graduated neural density 0.9 soft
- graduated neural density 0.9 hard
- graduated neural density 0.6 reverse
- neural density 4 stop
- graduated neural density 0.6 soft
- graduated neural density 0.6 hard

at least you can order sets of filter from adorama.com, which saves you some money and I don't need any warming/cooling filters. Cause I can do this in gimp.

also everybody recommends to stay away from cokin filter, cause they have a magenta color cast. So they recommend hitech, lee, singray.

further there is also the third possibility, you can simulate the effect in gimp and photoshop with multiple exposures. So I only need to buy a polarizer. I will try this for the beginning and save some money until I decide what todo with it.