Hi kimi kimi,
I'm researching this topic for quite some time now but haven't installed one yet. So take my responses according to that π
First of all i strongly recommend reading this Guide to GPU Rendering by Chaos Group. From background reasons to rendering advices, it's a great article (It's for 3ds Max but general idea applies for everything). Half of your answers awating you there.
1- Check this manual for Supported Features in Interactive Rendering in V-ray for SketchUp.
2- They're all technically gaming cards, aren't they? And i don't think there is a specific one for Sketchup + V-ray combination. You can check this website for GPU or CPU comparisons: http://www.videocardbenchmark.net/ . There are lots of useful charts to examine. Another benchmark result for GPUs from Furryball. Also check this website for helpful articles: http://www.gpurendering.com/
3- I think yes, it works.
4- 5- 6- no idea
7- SSD makes them load faster just before render for sure but i doubt you'll have enough space for all the resources from various works (You can use SSD only for resource heavy works maybe). You need to decide whether that load time is on your list of priorities or not.
8- I would like to hear as well π