A couple of points..
1) Hi, and welcome. This is a good forum, and I think you'll enjoy it.
2) If you go to a bike shop, you can test ride a variety of bikes, and they can help determine what your size is. I see a LOT of guys buying a bike that's too small and then running into problems.
3) 2 or 3 weeks after you buy the bike, the cables will stretch, spokes may be imperefectly tensioned. It will need a mini-tuneup. A bike shop will do this free if you buy it there. If you don't the cost will be about the same as what you saved buying online.
4) Bike shops often give discounts to buyers. You will need a helmet. Most wind up getting bike shorts, or a tail light, or any of a number of different things. One accesory I like that the Continental had 30 years ago is a second pair of brake levers on the top of the bar.