You won't know until you try but the pain in your feet and back is relatively normal. You'll always feel very tight and achy in the mornings but once you start hiking and get warmed up the pain goes away for the most part.
When it comes to fitness, I'd say just get on the trail and start hiking. You'll soon lose any excess weight as your body tries to keep up with your calorie consumption. Just take it easy for the first couple of weeks.