T900 rear OLD=145 mm. A standard MTB rear wheel (OLD=135 mm) is not compatible without modification.
At your team weight, you can certainly use the lighter front wheel. And, as TandemGeek suggests, lighter tires are readily available. If you ride primarily on the road, consider the Bontrager "Road Warrior" 26x1.25. The sidewall says 45-85 psi. We run 'em at 100 psi on our triple, with a team weight of 330 lbs/150KG.
We do not own a T900, but that won't stop me from offering this opinion: A suspension fork will add weight, complexity, and cost. It will also change geometry and handling. If you do not ride off-road very often, you can surely do without one.