Correct, Nvidia cards are unable to use the open freesync technology. You want to look for a monitor with G-Sync technology from Nvidia
Answer 1: I have the flat version and a buddy of mine has the new (slightly) curved model. The curved verizon seems a little more immersive, but it's not as noticeable or valuable as the having a curve on an ultrawide monitor.
Answer 2: In most of the videos I have watched regarding refresh rates and G-Sync from LTT, everyone seems to value G-Sync much higher. I am not familiar with the power of your rig, but a 75 Hz monitor with G-Sync would be very enjoyable for playing games at 1080p or 1440p. The step up to higher refresh rate or higher resolution while keeping G-Sync technology seems to bring a very large jump in the price tag as well. With that being said, there are still noticeable improvements in the gaming experience and it is ultimately up to you what you want to spend your money on.
Best of luck on your quest.