Welcome to TE! I think you'll find answers to just about anything you might be wondering about here, and then some, but I'll just say one thing since it crops up often:
don't think you need a big, cushy saddle because you're heavier than some riders. The size and shape of the saddle has very little, if anything, to do with how much weight you're carrying on the outside. If you don't believe me just check out any bike rider from behind, and see how narrow the saddle is compared to the total size of anybody's butt

A comfortable saddle is important for comfortable riding. It has to be wide enough to support your sit bones, but narrow enough to avoid chafing. Any good bike store will know this, and if they don't say anything about it, ask.

Oh, and a bike is a fantastic way to work out while carrying extra weight. I carried on biking up into high pregnancy because it was by far the most comfortable way of moving and getting some exercise.