Heating:

Is heating necessary for killies? That is a good question because it depends. Which killi are you choosing and what room temperature you are able to give them. Some killies are best in 15 degrees and some in 25 degrees. In my fish room there is about 22 degrees at day and about 19 at night. When the light tubes turns on the water temperature rises together with the room temperature up to around 22 degrees before it starts fall down to 20 degrees again. This kind of temperature changes is not problems to the killies. The same is happening in the streams and water holes they come from. But if you need a constant high temperature for your killies you will have to either warm the room or use a heater. Warming the rooms maybe sounds a bit crazy but if you have plenty of tanks in your fish room it is often more economic to heat the room than to heat all the tanks with heaters.

Filtration:

Filtration in your kilitanks are actually not needed, if you have only a few fish in the tanks and use plants and frequent water changes. Many killi tanks are completely without any filtration and 50% water change each week does the job to keep a good water quality.
But there are many cheap solutions for filtration so I always use it. For bare tanks you will have a great solution with small filters with air lift. You only need a piece of filter sponge and some air hose to make a good helpfully filtration system. I chose the easy and still quite cheap solution. Bought a larger air pump and some Biofoam sponge filters. I still change about 30% of water each week and "clean" the sponge in tank water once each month but my water quality is much better than before the sponge filters. Please remember not to clean your sponge completely as you have valuable bacteria in the sponge. Only the worst debris and visible dirt must be cleaned form the sponge.

Typical small sponge filter

If you want gravel in your tank you could also consider under gravel filter. I have used under gravel filter with air lift in some of my tanks also but I am changing away from it because I do not want the gravel. The filter is very good and you can get very nice water quality with this filter, but you have to accept to have medium fine gravel in you tank for using it. Many killies will place the eggs in the gravel if possible so you will have no possibilities to collect the eggs from the tank. As you can imagine, this could be quite problematic if you want to breed your annuals. For non annuals you will not have that big problems with eggs laid in the gravel unless the power of the filter is too strong, If you use a powerhead to pull the water you might such the eggs through the gravel with no possibility for the fry to find a way back. If you use slow running air you will have a perfect filter for your killitank with gravel. Another benefit is that you can have more different plants in you tank when having gravel than in a bare tank. Some might say that under gravel filter and plants is not a good combination but I have had great success with plants like Rotala rotundifolia, Hygrophila polysperma, Vallisneria spiralis, Limnophila sessiliflora - all planted in the gravel.

My air lift tube for the under gravel filter.

Another solution could be motorized filter pumps. The habitat of many killies is still or slow running water. Following it is not always a good idea to make too much water circulation in your killi tank. A small hanging filter or a minor inside filter could be suitable. Just make sure that it will not suck in the very small new hatched killi fry.

Plants will also help you with your water quality. More about plants here.