Hay there Bear, I am a retired Fire Chief. After you read this your going to think this is crazy, but burning down your house is way more worser. There are some things you need to do to make this safe. Lets start with air. You mentioned Positive Air flow. Absolutely a great idea. I would recommend a heat exchanger so you can pull outside air to create the pressure, because you will exchange your houses air multiple times an hour and if you run AC or heat for your house you truly will be heating or cooling the neighborhood. The idea here is to provide an air flow from your point of egress to your forge. I would also put in a forced air exhaust fan, just incase. As far as heat source Induction is absolutely the safest, if your house wiring is up to the job. If your going to use a gas fired forge I would recommend an automated fire suppression system that disconnects the fuel from the forge, most folks call this an Ansul system. You may get away with just a fuel cutting system. The Fire load in your shop will drive what system you need. For obvious reasons I would keep any combustibles well away from the shop. This includes your clothing, you don't want to be a flaming screaming MEME running through your house looking for a hose. If your going to use Coal, make sure you have a heavy cover. May want a sprinklers. There's a product http://pinkshield.ca/ I would install this on the ceiling of the basement and any exsposed wood. Also there maybe a need to install spark arresting curtains. Above the forge heat shielding is a must, and around the forge if you have any wood. I would recommend http://www.rockwool.com/business-portfolio/Rockwool-building-insulation/ be installed over and around your forge. This material will not combust under normal fire events and I would put it a least two inches behind the heat shielding and over wood. Make sure you have a clear Egress plan, like the kind you have for your family. Do not exhaust your forge through the the hearth unless you install an approved flu pipe from your forge all the way to the top of the flu. A certified Chimney Sweep can help you with this. Also Carbon Dioxide detection devie is paramount. Above all I would check you local building codes, life safety codes and your local Fire Department, good luck friend if I can be of any further help please let me know.
Regards