I want to restore an old house, should i keep original or is it wise to change it slightly?

If you want to get help funding from a historical society then you have to keep it all original. If you are looking to turn it around and sell it the trend is open floor plans and many bedrooms. The bedroom addition would be a great investment! You have to be careful with the attic as a bedroom because there are fire codes saying that you have to have an alternate escape route if you make another bedroom in there - like a window. Also bathroom additions I've heard bring up the value and having a master suite. Definitely bring all of the plumbing and wiring up to date. To make sure you could turn it and sell it just do some research on what makes homes more valuable in today's market. Sounds like a fun project! Good luck.