Hey BigDLou, be welcome to TeamEstrogen! This is the nicest of place and no question is stupid and nobody is lame here.

(And actually you know what, many people think it's very cool to ride a bike with no gears. There's even a web site of cute guys in their underwear with single-gear bikes, don't remember the address however... oups! am I disgressing?)

So I'm with all Singletrackmind said so I'll just answer (in parts) two of your more technical questions first and let people who know more tell you more.

300$ bike? Yes sure. You can find a good hybrid for that price. I had a Trek7200fx that I loved and paid 350$ canadian or so. It was the bike that started the love story for me. I strongly suggest a local bike shop where you feel welcomed though, more than a bigger place/general outdoors store. But above all go where you feel that the staff is helpful and friendly. But don't feel too self-conscious: there are tons of plus-size riders out there, and you're certainly not the "plussest" of the "plusses" (check out the recent issue of Bicycling magazine from your local library on this). (I hope you understand my late-night English there...)

You can always get a better bike later. But 300$ will buy you basic, good quality components.

Gears: they're great. They help you up hills and when you have a headwind. There's many threads on this topic here, I'll end up making a web site with this information because it gets repeated a lot. Just remember that 1) you need them (unless you're so cool already that you don't, just like the boys I was writing about above!!! ) and 2) you must experiment with them to get familiar with them and also that 3) nothing can explode while you experiment with them, and it would be VERY hard for you to break anything by just shifting.

Come back with your questions about the gears when you have started using them a bit, you'll get tons of help from the WWoTE (wise women of teamestrogen), I promise.

Enjoy the ride!