The Trek FX series is highly touted on these forums, and would probably make an excellent starting point. The 7.2 retails for $549 USD and has decent, entry-level components. Skinnier tires are usually fine... depending on riding circumstances of course. The 7.2 comes with 35mm tires, which are actually quite "fat" compared to many bikes out there. For the record, I ride on a bike with similar geometry that has 32mm tires and they handle my Clydesdale frame just fine. Saddles are a very personal choice, but keep in mind that wider is not necessarily better. A saddle that is too wide can push your thighs outward and make you a less efficient rider. Most bike shops worth their salt will allow you to try a few saddles to determine which one you like best.

Most importantly: Test ride as many bikes as possible! A bike that isn't a joy to ride will sit in the corner collecting dust until you sell it for a fraction of what you paid for it.