On question #1, your best bet is the Apple Support forums. If there an issue, it should have been reported there by now.
On question number #2, you can ignore the server stuff and use the Mini as any other Mac with OS X Lion on it. You may need to tweak the default firewall settings but that is all I can think of.
On question number #3, I have heard on different podcasts that people include both SSD's and HDD's in their Macs exactly like you want--system files on SSD, user files on HDD. Other World Computing is a good place to find SSD+HDD kits for the different Macs. I do not know if they offer one for the latest Mini, though.
On question #4, I cannot talk from experience with the current Mini. However, looking at its place within the Mac lineup alone, you can argue that eventually the Mini becomes their least capable Mac. While today's Mini has a recent Intel core architecture, and while you can in theory use a Thunderbolt drive as scratch disk when working on FCP X; just from my experience with the original Mini, I'd say that it will eventually fall short for your video editing needs.
Hope this helps.