You shouldn't have too many problems nesting in your painted house as they don't care fore painted or pressure treated wood. Bare, unpainted or weathered softwoods are preferred, especially redwood, cedar, cypress and pine. So to provide them with a nesting place just get some boards or blocks of any of the above softwoods and hang or attach them where you want the bees to nest. It might be good to have a space or separation between this nesting wood and your house to avoid having them burrow into your house. This could be done by putting a piece of flashing/metal between the nesting wood and your house or leaving an air gap between the wood and your house.

You shouldn't have too many problems removing the porch. While the males may act aggressive, they don't have a stinger, and the females seldomly sting. Still removing their nesting area is a pretty big disturbance so some caution is advised. If you can wait till cooler weather and they have left or are dormant you won't have any problems at all.

If you are removing the porch you could save the wood and hang it back up since they already appear to like it as a nesting place.

-Tim

Here is a link that might be useful: Carpenter Bees