Two bedroom homes can be harder to sell. In Hopkinton today, there are six two bedroom homes on the market and four of them without garages and two with two garages. I would suggest you contact an agent to give you an indepth market profile. Call me if you want my help.
It would really depend on the condition of the current house (upgrades etc) and the lot. It's hard to answer that question without knowing what the "base" house is prior to the addition. Adding a 3rd bedroom but losing the garage might not make a huge difference in your market value.
Have you thought about turning the house into a rental?
That is very property specific question. Without knowing the actual layout of your home or the potential in the garage, I would not be able to stear you one way or the other. I can tell you that making an offer on another property with a contingency is difficult to get away with these days. As I tell all of my sellers, selling first is the best way to maximize your negotiating power on both transactions. When caught in a sale contingency you may be forced to over pay on the buy to lock up the new house, and then take a lower offer just to get your home sold.
Here is a link that will give you a loolk at the 2 bedroom market in Hopkinton. http://www.marketsnapshot.info/reports?cnsmr=False&Repor
If you have any other questions please don't hesitate to contact me.
Hayden Rowe Properties
That is a hard question to answer wihtout knowing your current situation. If your current home meets all your needs: location, condition, and value, then it might be worth keeping. Taking a garage and turning it into living space is doable. Is the garage attached or does it have living space current above it? If you can live wihtout a garage and that is the only added space you need, then it seems like an inexpensive fix. It really comes down to preference and where the garage is located.
Best of luck,