Laurie, I'm far from being an expert but I love talking about running so I'm happy to answer your questions the best I can!!
1 -- Shoes are important. I went to a running store at the beginning of all this, when I was just doing a few minutes of running in my walking, and I got a pair of $85 Brooks running shoes. They felt wonderful for months. They got me through the first few months of running and even my first 10k. I got a second pair of the exact same shoes and they felt HORRIBLE. I ended up with serious foot pain and went to a doctor, who told me to get fitted by a pedorthist for shoes custom fitted to my feet. I ended up spending $168 and two hours of being fitted, but it was WORTH it. The pedorthist told me that I was in the wrong shoe originally but I was so heavy at the time that I was sort of controlling the shoe instead of the shoe fitting my foot, if that makes sense. When I lost a lot of weight and upped my mileage, my body changed and the demands on my feet increased, so I needed a better shoe. Long story short: you may be getting by on cheap shoes now but you're going to need good support or you'll risk injury. Every seasoned runner I've ever talked to has said that good shoes make all the difference in staying injury-free.
2 - I started running at 250 pounds, and my knees hurt a bit from the impact. I iced them at night when they hurt, and I got through that pain in a few weeks. I can't say for sure if your body will be ok with running at your weight, but mine was certainly fine. At around your weight, I started training for my 10k, and I ran it at 195. If you want to run, do it -- don't wait!! But get good shoes!!
Let me know what you decide and keep me updated on your running. You should also check in with the Cool Runners thread in the Exercise forum, if you haven't already. Great place to hang out.