The #1 thing you need to accept is that it is going to be hard work, you are going to want to stop and it is going to take a long, long time. It is inescapable, whats done is done and you are at where you are now you just need to make sure you have enough spirit and motivation to stick to a good schedule even if it takes years.
Also on the subject of bike riding i found it very helpful for my legs, i lived about 7km from my school and would walk home every day but apart from being boring it did nothing, when i finally got a bike it took about 2 weeks to put enough muscle on my legs to show easily without any tensing.
Also it will be helpful for you to know what kind of body you have, i can't remember the names for the different types but I am the kind where it is difficult to lose weight but i put on muscle very easily.