I'm about the same height you are ... but I'm not "severely overweight." (I hope to be, and by the end of the year!)
The best way I've found to keep from being overwhelmed by numbers is to break things down into chunks. I don't know if 25 pounds is your short-term or long-term goal, but either way, you might want to consider setting a series of smaller goals that feed into your larger goals.
Five pounds at a time is a lot less overwhelming than 25. (I'm going with 10 pound increments, but either way.) I find it easier to tell myself that I'm going to finish losing the next X number before I worry about anything beyond that. And when I hit a mini-goal, I celebrate. (My first celebration was a $15 chair massage.)
And I think you've taken a huge step toward your own success by joining 3FC. This place is AWESOME for inspiration and motivation.
Good luck to you!