Michiel,
I think it's a good idea to use ambient heat produced by incandescent bulbs. I personally do not like the look of the red lights so I use the blue night lights made for reptiles (get the spot light type bulbs which direct the temperature), these cast a very pleasant, 'natural' looking light. If your local pet store does not supply them, or in insufficient wattages, you can order them from many of the herp supply companies advertised here.
I'm going to assume that your setup is large and that the lights are inaccessable to the snakes (a false top made of a heavy mesh with the mesh size small enough that your little guys can't crawl through). I would not use a timer or a thermostat that turns the lights on and off; you'll get much more life out of your bulbs if they burn 24/7. Use a rheostat with the sensor located at the hot end and have a lower watt bulb over the cool end. Keep your babies in rubbermaid containers as described elsewhere on this forum until you've got your main cage dialed in. If your cage is tall enough, put in branches and shelves so they can utilize the vertical temp. gradient.
Keep seeking advice; this is a great forum to learn from.
Good luck,
Paul