If I can't get to the gym and I still want to work out, would it be a suitable workout to work my core with exercises that I can find on line. Ex. the Plank and others. Or is there possibly something better?

The magic word here is "calisthenics". These are the exercises like pushups, situps, etc.

Here are my personal favorite ones for core.

1. Flutter kicks

2. Bicycle Kicks

3. Side Planks

4. Russian Twist

Remember: you can do these core exercises all day, but it won't give you a six-pack. Cardio does that that.

Kit,
I'm thinking it's going to be darn hard, a probably a long time before I can accomplish my goals. Right now, I am pretty weak and I think I have age working against me as well. I have a substanial beer belly that I developed over the last 25 years or so. I just figured by trying to develop my core that it would help me be able to work harder when I am in the gym.