Until one of our local electricians reports in I'll offer this:
1.) Due to the age of your home the first question that comes to my mind is: Are your walls and ceilings plaster, or are they drywall?
If they are plaster you could be asking for trouble doing this yourself. Plaster ceilings can be very difficult to deal with when trying to cut holes in them without wrecking the ceiling.
2.) You are aware that "can-lights" don't really project light throughout the room but they project more towards the floor instead?
3.) You could pull the necessary power from the existing circuit using the same switching you have now if you want everything to come on at the same time. Messing with the switches you have can be very tricky.
4.) How about installing some track-lighting on the surface of the ceiling? That wouldn't require much in the way of new holes.
5.) Do you have access to the ceiling cavity for fishing additional wires?
6.) I'm guessing you could probably add up to about six hundred watts of additional lighting before requiring a new circuit assuming your current light circuit isn't running some wall outlets somewhere.