To develop and tone abs, is my best bet to stick with just one relatively difficult excercise (bicycles) to max, pause, and then go at it again. Or cycle through several excercises (bicycles, crunchs, reverse crunchs, etc.)?

Seeing as they'd all excercise the exact same muscle, I don't see there being a real point to needing to vary what excercise I do, but perhaps I am wrong?

Ive seem to post this in many threads today so here you go mate.

At the end of the day mate doing abdominal exercises do not give you a six pack they only strengthen the abs which make them a tad more visible. If its a nice cut stomach you want then do lots of cardio which will lose the excess body fat and give you a flat stomach.

The reason i suggest cardio and not the exercises is because you cannot spot reduce as in you trying to lose the fat off your belly.

Cardio exercises range from running,jogging,swimming and many more.

Have fun train hard

Indeed. First you need to loose the fat and then tone the abs. Everyone has muscle on the abs, just some have it covered by fat. If you take the fat off, it is there. Like all muscles however, they do get bigger and stronger when excercised. Do lots of cardio, and:

-Do very slow situps/crunches 2 days in a row, and allow 1 day for muscles to repair.
-Watch your diet.

Erind.

You need to do full body work outs, like running if you want to lose significant amounts of fat. Why total body? I once read an article that described the human body like a lake. The water in the lake represents the fat on your body, if you wanted to see what was below the water in a lake would you try to scoot out the water in that one part of the lake an expect to see the bottom in that one part of the lake more quickly? No, you would slowly lower the entire level of water in the lake. The same can be said for the human body, if you work only your abs, you ab muscles will get bigger an you will gain muscle but the fat will still cover those muscles an you wont see the gains you are making.
You will lose fat if you only work specific muscles like your arms or abs, but to really see results an lose significant amounts of fat you need to run or do aerobic-type exercises. You could do crunches/ab exercises all day long an not burn as many calories as running for 20-30 mins. Total body workouts like running will increase your metabolism an burn calories much more quickly than any other exercise. An thats how you lose fat with calorie deficit, burn more calories than you are consuming.
You also need to watch what your eating, exercise an diet are both equally important.
I used to be a bit over weight myself. I started out walking 2 min, light jogging 5 min, then walk 2 more min till I caught my breath again, then jogg again for 5 mins till I could jog 30-45 mins non-stop.
I weight train 30-45min then run/jog 30-45min 3-5 times a week, but at one point I was running 30-45 min 6-7 days a week. An making sure I was eating low fat/ low sugar diet with significant amounts of protien.
On the diet side, try to avoid sugar it hurts your body's ability to burn fat because your body produces insulin which is used to do 2 things. 1)Control blood sugar levels an 2) is also used to burn fat naturally in your body.
If your blood sugar levels are high, like you drink a soda before or after your workout, it will significantly dimish the fat burning you would get from your workout if you didnt drink that soda.
But there are 2 kinds of sugar one is ok the other one is bad. Sugar you find that occurs naturally in fruit wont cause large increases in your blood sugar level because its naturally occuring (fructose) an gets digested more easily than refined sugars you find in Soda, Candy, ect.
You most likely have wash board abs, you just need to melt that fat away in order to see them. If you killed yourself running an eating right, it could take ya a month or so but the results will come.