Holy heck Tink and believe...you guys are kicking some serious butt already....
Maybe you need Marine basic training
Ok here goes....
Tink- Your eating is great... can't really do much with that so we have to do the excersize... It sounds like you are doing mostly aerobic excersize.
Your challenge.. 3 times during the week you need to add 45 minutes of free weights or machines, concentrating on a different mucsle group each time. Please get some help from a trainer if you haven't done much of that before, the last thing you want to do is injure yourself and not be able to keep up the good work you have been doing.
Believe...congratulations on achieving your goal!!! You must be so proud

Maintaining is where it is at!! You don't want to become a yo-yo dieter after all your good work.
Your challenge for one week is to go back to doing EXACTLY what you did when you lost the weight to begin with. Don't even think about it, pretend you are back at the begining and just do what you did.
For excersize (and this assumes there are NO medical reasons you can't) you can add some aerobic excersize. The walking is great. Start with that and build on it. Three times during the week just do your 4 miles but start picking up the pace a little. Let it come naturally, just jog for a while and when you are out of breath go back to walking. As time goes by you will increase the time you run untill you are running the whole time.
That will REALLY help on maintaining the weight.