check this vid   https://www.youtube.com/watch?v=EWVyutw3hZk     and also see following videos to get some idea how GPU rigs are built.. cheers

Motherboard Asrock H97 Anniversary will work and have 6 Pcie slots

Raisers https://www.aliexpress.com/item/Best-quality-PCI-E-PCI-E-Express-1X-to-16X-Riser-Card-USB-3-0-Extender/32652540906.html?spm=2114.13010608.0.0.6VDfOc

lot of 20 raisers around 90 USD including shipping. good deal.. i brought a set 2 months back and are very good..