Q1: Use the timing control. Otherwise you're only getting half the benefit of the system. Also, it is pretty cool being able to adjust your timing curve to what the car likes. I'll echo what @mikeyhunts
said, the sniper and either the dual sync or the hyperspark are the bee's knees. While I was able to use an MSD pro billet, it was not nearly as user friendly as those two options.
What intake manifold do you have? If you have a dual plane, there is a reasonable chance that the sniper wont play well although a carb spacer generally solves that issue. If you have a dual, see if it has the divider milled down (like the air gap generally does). If it does you should be g2g. Mine did not and I have since swapped to a single plane.
Why did I end up changing? I ran into an issue where the Sniper would not meter the side that didnt have the o2 sensor very well. When I say "didnt meter very well", I mean it was 2 points lean and would misfire. I couldn't add a spacer since I have a 408w and hood clearance is an issue. Swapping the intake fixed the problem.
You'll also want a fuel filter but you probably realized that already. I have an Aeromotive 340 Stealth tank and dont have any issues. It's a Tank's INC tank with Aeromotive pump. I do not know anything about the Spectra tanks but, Tanks INC is a proven design for our cars. I'd probably look at them first for your application. Word of caution; Walbro pumps can be loud.
If you have electric fans, there is no reason for you to _not_ use the built in fan controls. You should have relays already in place, it's really easy to hook up, and is slicker than snot on a brass door knob. I have both my fans wired in and it's amazeballs. I also have one fan on an override switch but i doubt I will ever use it...more as a safety net.
I have no opinion on your AC conundrum. Classic Auto Air might be able to hook you up though. I'd give them a call and see what they can do for you.
'One at a time or together'...depends really. If you are wanting to keep your installation clean and mount your sniper wiring to the underside of your cowl (like I did...see my build thread), you'll want to do it BEFORE you put in your climate control. If not and you're content with keeping most everything in the engine bay, then dealers choice. Also depends on where your battery is...mines in the trunk which made running wiring a bit more of a challenge. I ended up mounting a battery junction under the dash to simplify things.