Being heavy doesn't always equal being out of shape. I have fought being heavy the majority of my life. The only time I have been skinny was in college and I starved myself thru a combo of walking everywhere (no car), poverty and smoking a pack a day.
I still weigh too much. I know it. But, always, the Drs and nurses underestimate my weight by 20-30 lbs. Why? I have a lot of muscles in my legs, and I am not "sloppy" fat (yeah, like the fat ladies at Walmart wearing stretch leggings and Minnie Mouse T-shirts). My fat is well distributed (not sure if that is a good thing? Lol!) and I am lucky I suppose that I don't have a pear or apple shape.
But, anyways, my drift here is don't let it stop you from getting out. So your fat? Well, over half of the US is! At least you are trying to change it!
Spend your money on good boots, as noted. Your feet will thank you. Use trekking poles, save your knees. Excersice at home, even if all you do is walk. Walking trains hiking muscles.
Buy clothes that flatter you and get out!
I am amazed out here how many other larger ladies I see now on the trail It makes me very happy!
Sure, you might walk slower, but you'll still get there..eventually. So the mile mongers blast by you? Eh, no loss, you can enjoy the quiet time, listening to nature. And the mile mongers can save you a spot at camp!
This tubby can hike 19 miles in a day So no excuses! And I take high blood pressure meds that lower my heart rate even! Every step you take is one step to being fit (and I didn't say skinny!)