keeping muscle mass

I agree with the comments that most important is to lose weight slowly. This way you can realistically try to retaining more of your existing muscle through strength training and protein.

How? Losing weight slowly is simply about keeping the net calorie deficit (calorie intake minus daily requirement without activity minus exercise) to 500 calories or less. Should still lose a pound a week or so. Also bear in mind that a couple hundred calories either way on a given day is ok as long as you average to your goal calories over a week.

If you go quicker, your body hoards fat so you lose MORE muscle in proportion to fat. And worse immediately after going into sustained calorie surplus (if you don't control net calories at goal weight) you add back put MORE fat on in proportion .

In summary, I suggest you set your daily calories using the myfitnesspal diet profile goal set to 1 pound per week and eat back calories from exercise using the estimates in myfitnesspal. Though a bit dubious - better do this and then adjust a bit if you feel they are an overestimate than not eating them back.

Also prepare to maintain: When you reach goal weight be careful to adjust calorie regime and strength training to maintaining the lower weight / higher muscle content. If you just fall of the wagon it all comes back soon enough. Just set your myfitnesspal profile to maintain current weight and eat back any exercise calories you continue to burn...