New "Home PC" Build

[RahiSan]

Hey guys!

Im in the process of starting my own company together with a collegue.
I will move my current workstation (i7 4770, 2 GTX 780 6gb, 1 GTX 750ti, 20 gig Ram) to our office and need a machine for home.
I will be using it for some light gaming but mainly Modo, Zbrush, Photoshop and octane.

I was thinking about getting a single 980 Ti for it with the capability to add more GPUs later.
My question is which Motherboard/CPU configuration would be good of for my purposes.
I have a Budget of about 1400 Euros, but its my private money so spending less would be very welcome.

Also, if I do not intend to use my new and old machine simultaniously, do I still have to buy a second octane
License or does it work like Marmoset where I have to active and deactivate using different machines?

Thanks a lot!