Re: Risers: what is this trend to remove them and attach the GPU to the mobo?
but my bad experience with risers is that I use 4pin molex psu cable powering up 3 Risers wit GPU Rx480 8GB, and ended up burning the cable connected to PSU. 
Basically you have used a 3x splitter over a single molex cable?
I also read that sata to power the riser is generally a bad idea, this is correct?
Yes, SATA powered risers are the worst.
ALTHOUGH, I use SATA risers at the moment because that's what I could buy way back when I made my rigs. However, I use 1 riser for 1 cable to the PSU. Using 2 risers per PSU cable made the riser wires get very hot, and more than 2 will probably burn them out.
It's best to use 6-pin risers if you can.