Welcome! It sounds like you're off to a great start with your mindset. I believe that where your motivation comes from is a huge part of sustaining the success you'll have. I know that when I've lost weight for an upcoming event or just to look good for summer, I always gain it back, and in the last few months, I've felt my motivation shift from vanity to just being healthy. The external changes are just a byproduct of the new habits and changes you're making internally.
I'm so sorry about your father. I also have a diabetic father who has battled it for almost 20 years, while making no real lifestyle change. He's had a heart attack, quadruple bypass, cancer, and has been insulin dependent for about a decade. I am so sad watching him live like he is and knowing that it could have been so different for him. I also work in a diabetes research clinic, so I have daily motivation!
Also, I just wanted to let you know that I used to have back problems years ago before I exercised, and pilates changed my life. My issues were very minor in comparison to yours, and I don't want to recommend trying anything without talking to your doctor, but I had a lot of luck with Windsor Pilates. I ordered the DVDs years ago, and they had modified and shorter workouts to start. I didn't even really break much of a sweat, but it strengthened my core very quickly. It's all floor work on a mat, so I don't know if that would work for you, but I used to throw my back out regularly, and it's only happened to me once in the last five years.
I'm so glad you found fitday... it's a great resource, and can be wonderful for accountability if you use what it has to offer. I wish you lots of luck in your journey, and keep us updated on your progress!