Thanks for posting! If you can post some pictures that would be great.. Go to the bottom of the page and click on "advanced" it should give you an option for uploading a photo there.
Without seeing any photos or knowing more of your background I would assume the decrease in the glutes is due to the lowered volume in your training and probably the type of training and exercises you are doing. Also, in order for your glutes to grow you need to make sure they're getting enough activation and stimulation in specific exercises. I have always had troubles activating my glutes in my lifts, I am back and quad dominant in all of my lifts and recently found out my glutes aren't "firing"appropriately so I have been seeing a specialist here in Vancouver who does neural activation techniques on me in order to help... Now I am lifting more weight and my ass is growing, finally!
The issue of stomach leanness is going to come down to your diet. The phrase that "abs are made in the kitchen" is no word of a lie... It sounds to me like your diet isn't 100% on track right now but once you get back onto a strict nutritional plan then you'll see your stomach fat reduced. You mentioned that genetically you tend to carry weight in your abdominal area so it's likely that this is the last area on your body that you will see definition. Don't be discouraged if your abs aren't coming in as fast as everything else, it will come!!
I don't think it's an issue to accomplish both of these goals at the same time. You don't have to be fat in order to put on new muscle, you can be lean and still gain muscle(obviously not stage condition but 10-15% bodyfat isn't an issue). Are you working with any coaches now? If not, I would suggest to get onto a new meal plan that is designed specifically for you and a training program that is suitable to your needs and goals.. 3 days a week is on the low side, I would increase it back up to 4-6 if possible
For increasing muscle mass & strength while losing bodyfat Carbolin-19 is one of my favorite supplements and I think something like this would be perfect for your goals as well. If you haven't heard of it yet... http://www.T-Nation.com/store/products/Carbolin-19
Hope this helped you a bit and I'll wait for you to post some pics. Good luck