HI;
You are not much heavier than I was when I started seriously commuting via bike; now I am at 12 miles each way, every day; saving 1.2 gallons of fuel per day. (vehicle gets 20 mpg). Now I am a fraction over 300, and my waist is over 12" smaller.
As noted, purchase the bike you like, but pick one with 26" (ISO 559) wheels and 36 spokes in the wheels; I recommend against suspension.
I broke many spokes in the rear wheels, and because I am cheap; I learned to rebuild and then build wheels myself.
Immediately on your new bike; have them tension, true, stress relieve and re-true the rear wheel. This will maximize the life. Next, find out the length of the spokes in the rear wheel - the left (non drive) and right (drive) side will have different lengths. Purchase a full set of Wheelsmith SS14 spokes for the left side - unless you have a disc brake on the rear, in which case get DH13 spokes, and a full set of Wheelsmith DH13 spokes for the drive side. Make sure that you get 12mm Wheelsmith nickel plated brass nipples at the same time. Also purchase a good spoke wrench, like Park Tool, and the tools to remove the cassette or freewheel, depending on how your bike is equipped.
When (note, not if) you break a spoke, it will be on the right (drive) side. And in very short order, all of the spokes will fail, even if you replace them one by one. So when the first one fails, replace all of them with the Wheelsmith spokes, one spoke at a time so that you can put each in where without major figuring on where it came from.
Procedure for replacing them one at a time:
* remove the wheel from the bike
* remove the cassette/freewheel THEN remove the tire and tube.
* loosen all the spokes 2 or 3 full turns (720° to 1080°) - all the same amount.
* remove one spoke at a time, and put it's replacement in. Tighten the replacement so the nipple just barely covers the threads on the spoke. Repeat until all the spokes have been replaced.
* true it up as best you can.
* tension, stress relieve, true, repeat. (if you are not ready to do this, take it to the LBS, and have them do it)
Stress relieve is critical - especially for us big guys. Those flywieghts that disagree just don't knw.