Sounds like you have some great goals for the future, and it is okay to modify the plan for your individual needs.  Start out walking/jogging on a regular basis and then increase the time/mileage as you feel comfortable.  Go ahead and look forward for a 5k in your area and set that race as an objective to enter and complete.  It is great motivation and will assist with focusing forward.  Also, consider connecting with a local running group/club.  This is usually a wonderful resource to connect with others, participate in classes or just join up with some partners that can assist with your personal training. 

Wishing you all the best!

Echoing what Jasko and Haselsmasher said....

Start with brisk walks, that should tell what shape your respritory system is in, and where you should begin to stay comfortable.  If you struggle with motivation, find a 5k event about 2 to 3 months out and register for it.  Then set multiple smaller atainable goals instead of one large goal.  For example, one of my goals when I started running was to increase my mileage by at least a 1/4 mile every 10 days.  Mentally it's easier to accomplish that vs. having the goal of one day being able to run a 5k (3.1 miles).

Document your progress too, there's a TON of motivation is seeing where you've come from, but keep it simple....date, how far and how you felt is good enough.  If weight loss is a motivator for you, document that too.

....and keep reading these boards.  Lots of uplifting stories here with good people to lean on.

Cheers, and good luck!!!

-B