If I have a minted seat and would like to buy more seats, will those seats be added to my minted seat address?
Not automatically, but you can list whatever you want as the distribution address for your online seats, including the Minted Seat coin's address.
Will I still be required to log into the website every so often If I own a minted seat and buy seats that are not minted?
Not logging in wouldn't effect your Minted Seat, but after a period of time your distributions for online seats would be held. This is to avoid NastyFans sending BTC into a black hole forever in the event you were to cave to your mortality or a similar event.