I've ridden all the "Puffers solo on a singlespeed hardtail.
I did the first 2 with front suspension, but the last 4 years I have been on a rigid. If you're used to riding SS you're out of the saddle a lot so suspension is just extra weight to cart around. The only place where suspension may help is on the longer descent where stutter bumps get caused by cowardy cowardy custard heavy braking types on full sus bikes. There's usually a reasonable line at the edge somewhere if you don't like double vision. 
As far as gearing is concerned, there's 2 choices.
Keep your normal gearing and be prepared to walk in places later in the race (they only count the laps, not how you do them).
Or use my tactic of the moment which is to gear lower than a low thing to preserve energy. Maintaining the ability to keep going is as important as sheer speed to me. Of course if you aiming for a podium finish, nothing I say is relevant - I just aim to survive and keep going.
The bulk of the climbing in the course is from the start - one long drag, not particularly steep anywhere, but a real morale sapper at subzero sleety 3am when instead you could be standing around next to a nice warm log fire drinking coffee.
Ice tyres & spare brake pads are handy things to have with you.
Oh, and take tissues for the weeping gearies trying to re-assemble their mangled derailleurs with frozen sausage fingers by the light of a dimming LED* ... 
*It's not that bad really, but there's usually evidence of 2 or 3 destroyed derailleurs when you go round the course in the next few days after.
