I don't know that specific bike, but it looks similar in style to my Giant Sedona, so I think you will be happy with it. I started riding at 365 pounds, and I now have stabilized at about 310.... That is about to change with the new cycling season.
I will be moving to a Cannondale touring bike I have as soon as my gut is out of the way enough to do it... I expect that to be in another 50 pounds.
The Sedona has served me well, as I expect your Marin to do.
Now the trick is to find that balance between taking it easy, and pushing yourself... Do not be concerned if for the first few rides or weeks you aren't able to ride very far... It will improve.
Keep you pedal cadence up to avoid leg problems, and be sure that rest days are part of your routine.
Build up your mileage gradually (I have heard 10% more each week is about the max, but for the first few months, you can probably manage more) and before you know it you will be riding 20 miles without any problems. Within about 18 months of starting, I rode my first metric century (actually a little extra, a total of 68 miles).
By the way, I am 49, so I would encourage you to keep up whatever routine(s) help you to lose and maintain your weight... it doesn't get any easier.