Great to see someone getting into the sport. Earlier this year when I started riding a MTB on the road, I impressed the heck out of myself with 8 to 9 mile rides. I thought I was really doing something impressive. Now it takes me 10 miles just to get warmed up. You will get there too.
If you stick with it, you will lose weight. If you watch your diet, you will really lose weight. The more you lose, the faster and farther you will go. Once that starts to happen, you will upgrade your bike. I realized this need in about 2 weeks and bought a Schwinn Circuit. It is a solid and on the heavy end of the scale as road bikes go. Everyone wants me to upgrade to a better bike as my capabilities are greatly exceeding the bike but my goal is to be under 200# before I upgrade. That will be in the middle of next year I suppose.
The good news is that my contract goes away in February which means I will be unemployed. The better news is that I have enough in savings to cover all of my expenses for next year.
The best news is that I will be able to ride every single day next summer.