There are guides for installation in FS Open Support, but basically,
You don't need to install FS1, ever. You can play the full FreeSpace Port without it, and you can't use FS2 Open with FS1 Retail.
You can and should install FS2 retail, and then put the 3.6.12 binaries (you only need to pick one set of binaries to download, plus the launcher) in the FS2 install folder. You don't need 3.6.10 at all anymore.
Get the 3.6.12 MediaVPs, the latest BP:AoA, and BP:WiH, and install them in their respective folders.
You should already have OpenAL installed but get the TrackIR dll if you need it too.