1 - Only you can answer that, but I bought the same last week. It takes some getting used to after SH3 and I've not tried SH5 yet.
2 - Yes (as far as any ubi game is complete!) patched to 1.5 so the majority of mods are designed for this.
3 - I'm more of a U-boat kind of guy, so I've just downloaded OM, but there are many more to choose from. I played stock and didn't like it, at all but think the mods will once again make it a new game.
4 - Yes, I use W7 Pro 64-bit.
Specs wise, you've got better than me in everything except ram, and I'm running 2.93 Dual core, not 2.4 Quad. It'll do fine
