I'm about 50 lbs. overweight (225 lbs) I just started commuting 2 months ago, (10 miles each way), and have logged about 550 miles in that time, along with some weekend recreational rides on bike paths. Originally the 10 miles took me 55 minutes with lots of free wheeling down hills for recovery and an average top speed on flatland of a slow 12 MPH, and 2 months later it now takes about 37 minutes without any free wheeling recovery needed, and I can now ride vigorously for the entire duration and an average top speed of about 17 MPH. I have lost about 10 lbs without changing any of my eating or adult beverage drinking habits. So I would recommend you don't take the bus anymore, give yourself enough time to not be pressured and just ride the 8 miles, as vigorous as is comfortable for you right now, and your stamina will increase gradually.

I find that if I shower right before my ride, and change ALL my sweaty clothes once I get to work, I'm fine and smell OK throughout the day, the smell after the ride home (where I push even harder) is another story. Funny thing is, I happen to have a shower available at work, but don't use it.

BTW: Congrats, and keep reading this commuting forum, there's a vast wealth of knowledge here.