I'm sorry, but I have to disagree with Grover4. A male and female put together will likely kill each other too, because the male will constantly be trying to mate with her. In fact it is difficult to breed them because both of them must be well conditioned with live foods etc., especially the female, to survive the mating process and battering that it tends to involve. The female is always removed directly after egg laying occurs in order to save her life and protect the eggs. A male or female betta (one or the other) can usually be put with other fish in an aquarium as long as the other fish don't resemble bettas. Females can be kept together as long as they have been together from the start or introduce them at the same time into an aquarium, if you isolate one for a while it will establish a territory and if you bring another one into the same aquarium later they will likely fight unless it's a very large aquarium. If you're planning on just sticking to bowls, one fish per bowl would be best and healthiest. And yes you can put them next to each other for a little while, I would only do this after you're sure both are healthy and settled in as extra stress could increase the likelihood of disease.
Females, although lacking the long fins, in my experience are healthier and just as pretty - in fact when they get excited you see vertical stripes appear on their body, and if they are stressed you see horizontal stripes appear. Because of the male's bright coloration you usually can't see this phenomenon.
I'm glad you have a large bowl, this will make it much easier to keep clean and healthy!
As far as the heater goes, you can't use a regular aquarium heater in a small bowl like that. But what you can do is get one of those little reptile heaters that are meant to put under an aquarium to provide a hot spot, and put it instead under the bowl. If you decide to do this, keep the bowl out of direct sunlight and put a thermometer in the bowl as these heaters are not thermostatically controlled and could overheat the water, watch the temperature for the first day or so to be sure it doesn't get too hot. On hot summer days you may want to unplug it. A betta will do ok at regular temps (68 degrees minimum) but will be less active, more prone to disease and believe it or not, constipation. But lots of bettas are kept and do just fine at room temperature.