I finally managed getting my Fusion Drive Setup up and running with clover and yosemite.
Thought I share my experiences:
1. My boot problems have been caused by a corrupted fusion drive. At least this is what it seems like.
2. When starting over, I was not able to delete / create Fusion Drive via Terminal in OS X Install. As soon as it started making changes to a core storage volume, my pc resetted. This corrupted FD even further, I had to manually write to both FD disks and the unlink them. So do not use Install OS X Media to create / split a Fusion Drive!
3. There is no complete guide on how to make the EFI partition of the Fusion drive bootable on a legacy BIOS board. You can't use clover installer on a Fusion drive. Thus I wrote down what worked for me: See this post
Everything seems to be working now, using FakeSMC, Miezes Kext and Toledas patch.
Sleep works, but also wakes after about 2 hours for a short time. Not using DSDT until now.
Edit: I forgot I have some kind of "sound issue": after sleep, sometimes internal speaker out changes to "headphones" while no headphones are plugged in. It also stops output then until reboot. Ideas?