My new goal... fun run help. :)

Hi there everyone!

After completeing my first goal of losing 10 kilos I decided I needed to re evaluate and set myself a new long term goal. In my city there is a fun run next year late September. You can walk/run 3, 6 or 12km distances. I have decided that I will participate as my new goal. My best friend and exercise buddy has decided to join me which is awesome! I have a few questions for those who are more expereinced with this sort of stuff as i am a beginner in all forms, but I really want to do this. It is something ive always had in my mind.

I am currently 97kg, and 175cm tall. I exercise in short bursts of about 30-60mins at a minimum of 3 times a week at the moment but I am starting to include more and more the lighter I get as it is getting easier to move. What should I be doing to get myself ready to do something like this? Has anyone got any help? I feel a bit silly asking questions like this but I dont want to hurt myself or set myself up to fail.

Basically, what is a realistic expectation of myself in a year? Can I expect to be able to run the 12km or would I be smarter to just sign up for the 3 or 6? Or alternatively just expect to walk the majority? I would like to be able to one day run the 12km but I'm just not sure its a realistic goal just now as im still trying to loose the extra weight (BMI classes me in obese category, so a way to go yet!).

What do you think?