Congrats on deciding to lose weight by riding to work. I know it works. I lost 2 pounds a week for the first six months--around 50 lbs and have kept it off since.
As a commuting tool there all sorts of recommendations that will do the job well in this forum. You can get different opinions of everything from bikes and useful accessories to staying warm as winter nears.
As a weight loss tool I would recommend the addition of a food scale to measure portion sizes. Once I started using one my weight loss was more consistent. I attribute my successful loss to the scale as much as to the bike.