I am currently doing about 200 ab/core things a day.

I am 5'2" and weight 250lbs. Last body% measurement (hydrostatic) put me about 50% fat. I carry the majority of my fat around my middle and on thighs. I understand the principle of - 'you can not spot reduce through exercise'. So, how many ab/core things should I be doing to keep what muscle is in there nice and toned while I wait for my fat loss to catch up to my muscles? Also, going on the principle of progressive overload, do I need to continue to challenge my core for me to keep what I have built or would doing the same thing maintain what I have without more being built?

It maybe too soon in my journey to really make this switch - any thoughts on how to tell when to switch to a more maintenance resistance workout?

Honestly, I do very little ab stuff. All my ab stuff is through functional type things. I find that pushups and slanted pullups really use a lot of core/ab work. Also, I've started kayaking and found that it will make my abs a bit sore too.

I got up to 200 or so core exercises per day 5-6 days per week there for a while, and actually have cut those back dramatically. I do some type of core work now 3 days per week, usually in the 85-100 or so number depending on what I'm doing. I was beginning to think my waist was looking broader with all the core work, and I was up 1.5 inches on my waist measurement. I'm back at my original measurement now, and am focusing back more on fat burning exercises trying to decrease the hanging on tummy fat.

This is what I am starting to feel too. I'm not up any inches, but it is not going down really either. I know it will in time if I keep on program. Just not so sure I need to be doing as much.

Yes, I count pushups in my core routine as well as supermans.

Quiffy, you don't mention if you are also doing cardio and weight training? Along with your core workouts? I think that a mixture of all the exercising aspects would be the best to do. I do think you need to continue to challenge your core, but also the other aspects of workouts... Also doing the same thing will maintain to a certain degree, but you will also get very bored with doing the same thing over and over again...

Oh, yes I am doing more resistance training than just the core. Here is a typical morning gym workout

Elliptical: 5 Min

Squats: 1x15 no weight
Split Squats: 1x15 no weight, each side
Repeat Group 1x

Bosu Leg Raises: 2x25
Pointer: 2 x 30 sec each side
½ Push Ups: 2 x 10
Bosu ½ Push Ups: 1 x 10

Bent Over Rows: 1x25 10lbs
Shoulder Press: 1x15 10lbs
Hammy’s: 1x25 10lbs
Deadlift: 1x15 10lbs
Repeat Group 1x

Twisty Ball Crunchs: 1x50

Skull Crushers: 1x25 10lbs
Zottman Curls: 1x25 10lbs
Repeat Group 1x

Stepper: 15 Min

Evening workout:
100 crunches
random other stuff while hanging out - treadmill time, ball leg lifts, shoulder work

Rest days are Wen and either Sat or Sun. The other day of the weekend is not gym day but is at an active level with life stuff, shopping, cleaning, house projects - constantly moving for 6+ hours of the day. My job is a desk job so I get lots of physical rest at work.