NO to removing the oil boiler! You would simply add a coal boiler in series or parallel to the oil boiler, and use the existing distribution controls you now have on that system. NOW you have a multitude of options since you have one system that works in harmony with the other, existing system. If you chose to not run the coal boiler in the summer, you can shut down that side of the system and use oil only.....or some other form of energy to make hot water. If you look around the posts already here on the forum, you will see MANY pictures of installations doing just as suggested. Ask away, we can help...for free!!! Before you ask, yes, there are multi-fuel boilers, HOWEVER this is not required since you have a 10 year old WM. Your installation potential is textbook.....the chimney access is the next question.
I guess nothing has been said about your BTU requirements, but after a quick scan of the post, I'm guessing you are in the 150K +/- range and that happens to be the most common size boiler, anyway. Please don't freak out and obsess about how this can happen, we'll send you down a trusted, tested, and friendly path. Please feel free to ask here along with other pro's, just remember we are here to make you life simpler and LESS costly, not in the retail business.
If you would like to post your location, there are probably 50 coal burners right around you who would show you their set-ups......no charge....and greet you with a hand shake.
Independence Day tomorrow...and you are about to become MUCH more energy independent,yourself.