Hi Diki,
Well, first it is going to control softsynths like VSTS so no arranger with sounds are important as of now.
And if the keys are semiweighted that's ok.
I am thinking about getting an arranger like the Audya or T3, but not sure as I will start with this.
What prices may I expect for my criterias so far?
When it comes to music it will be various.