Regarding the Asbestos siding, from what I understand it will last a real long time. Many homes have asbestos siding, and I am pretty sure that it is very safe since the Asbestos fibers are "locked" into the siding and it is difficult for the fibers become airborne. Asbestos is a problem when it is friable (easily flaked) and the fibers become airborne.
Regarding lead - I'd call your state health authority and ask them about state and local regulations. Intact lead paint on non-friction surfaces is not a hazard - it is a potential hazard.
Ingestion of lead paint dust is the main problem in homes. It can affect everyone, but children under 6 are especially vulnerable since it takes less to poison them and they tend to put a lot of things in their mouths. In addition, their nervous systems are not fully developed and lack the protections that those over 6 have.
I think Joe has the best advice with the lead paint - to leave it alone as long as it is intact and watch out for cracking, flaking and peeling, especially around doors and windows (friction surfaces). If you need to do remodeling or it becomes unstable, the EPA has a good guidance document:
They say to have the paint tested first, but if you wish to avoid this cost you can assume that all the paint you are dealing with contains lead and treat it according to the EPA guidance.
Again, check with the health authorities in your state (usually the state health department)to see if there are additional rules. They also may have some suggestions.
Just a word about exterior lead paint. If their is lead paint on the inside of your house, it is very likely that there is (or was) lead paint on the outside. Even if it is no longer there, lead could have accumulated in the soils around your house. Therefore, it is best not to plant a vegetable garden near the house. If you are going to grow veggies, do it at least 10 feet or so away from the house. Save the area around the house for planting flowers and other decorative plants.
Hope this helps, again check with your state health department to get the specific requirements for lead/asbestos in your area.