Welcome to TE!!
I'm a physical therapist during the day and moonlight as a coach. Riding a bike is a great way to get back into shape while minimizing the impact on your joints!
Most people that are heavier do best on hybrids to start out. Then as you get fitter you may want a different bike. It's sounds a little crazy to buy one bike then another in a year but think of it as an investment in your health. Spending time an money on a bike will help to keep many heath problems away!
I wish I could find an article on line that I read in the Rivendell Newsletter one time. It was about a man who was a little over 500 lbs and had been told by his doctor that he had about 3 years to live unless he lost the weight. He tried walking but it was too painful. He started riding a bike but all the bikes he tried couldn't support his weight without breaking down. Rivendell (custom steel bike builder) worked with him to build a really beefy bike that would take his weight. He started out barely able to do 1 mile, but he tried to ride every day. 2 years later he was down to 230 lbs!! Less than half his former body weight!! This was combined with diet of course. He also had a rule that he had to ride at least 10 miles every day at that point. Even in the middle of a Minnesota winter.
Good luck on your journey. Please check in to TE often and let us know how you're doing.
Living life like there's no tomorrow.
http://gorgebikefitter.com/
2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS