decisions on sm100

Last night I started considering which bike set up to run in Stokesville this year.
I got a new El Mariachi 29er recently and have been riding fixed gear no rear brake for training rides. But 100 miles mostly off road in steep hills would be rough. Maybe freewheelin would work. Then what gear ratio? And then there is my soooory state of fitness. Sounds like my 1st sm100 in 2007 when I started training after new years day at almost 200 lbs. And I am only 5'6" soo 200# is hefty. I lost 40 lbs and finished the 100. This year should be esaier, right?
Too much beer. Too much pizza. yadda. 175# now. This is doable.
Back to set up question. Bike came as a 1x9. Probably my best bet but I so love to suffer and single speedin would serve it up. Can't decide.
Tires: bike came with huge 2.55" donuts. But they are heavy. On my no suspension rigid bike they are my suspension. But if I run my 32mm cross tires I will save mucho peso.
In my sicko thinking it will be SS with the 32mm tread.
Better see if I can do this. Looking for a fixed gear training ride on Skyline Drive this coming weekend with my 5.0m rollout gearing. 44x18. Gear is good arounfd Manassas and my training loop has 2 steep out of the saddle stomps, one is especially heinous where I must lift the forward pedal and pull hard on the bars. hmmm, we will see.