Had a pair of Blue Acaras breeding in my old tank - I understand they breed in exactly the same manner as Oscars. I wouldn't bother sexing them - venting is hard. They'll form pairs and then you know.
As for how often they breed, mine were prolific and it was a continuous cycle...I couldn't get them to stop. All they need is a flat surface - a rock is perfect but they'll dig and use the glass at the bottom of your tank if that's not available. I'd recommend putting a net over the filter intake so no fry get sucked in (they're not strong swimmers straight after hatching).
With mine, you'd start to see the male chasing the female around, some digging activity and then they'd lay their eggs on a flat rock and take turns fanning them. The adults share the workload and would be very protective, defending their territory aggressively. After hatching, the parents would put the young fry in a shallow hole. The fry would stay low in the hole (swarming around the parent). One or both of the adults would be with the fry at all times. If any fry moved too far away, the parents would suck them up and spit them back where they wanted them (very cute). As the fry grew, they got more confident and started swimming higher and moving away from the parents/hole. The parents continued to be protective for some time but, as soon as the fry became independent, they'd start eating them. In a tank with lots of hiding spaces, some wile fry might survive but not too many.
Within a week or two, the parents would be back at it again, laying eggs and digging holes. Of course, I imagine water conditions, stress, etc. would be a big factor in determining if/when they breed... Mine were really by themselves and had good conditions, so just never stopped.
If you want the fry to live, you just need to separate them early and raise them in a separate tank. I'd usually get them out as soon as they started becoming independent and swimming higher up and away from their hole. You will literally get hundreds - I had several tanks full of them. Do not try putting young fry in a mesh basket in the same tank as the parents; I learned that the hard way. The parents got distressed and tried to suck them out through the mesh to move them back to their hole, killing all the fry in the process. Definitely put them in a separate tank and feed them a fine fry food. They're easy to take care of and grow fast.
Oscars are sometimes sterile...but I think a lot of people assume it because fish in the wrong conditions won't breed. Get the conditions right and then you'll know.
