Building a rig, need advice

Hi, I'm planning to build a desktop soon and was wondering about some of the components. Would appreciate any help as I'm quite clueless in these.

1. I'm planning on getting two GTX980Ti, but I'm not sure which version to get. The store suggested the MSI variant, but I'm thinking about GIGABYTE or ASUS. Any suggestions?

2. Is two 8GB DDR4 Ram enough for gaming?

3. Is two Ssd in raid-0 a must? Does it improve the gaming performance?

Thanks in advance