Well it's going to be hard for any of us to tell you what is best for you. What would you like?
First thing to find out is will a bank allow you to become an investor and give you a second home loan. Watch out your current loan may have a clause that increases the interest if it is no longer a home loan.
I wouldn't do the extension now, you can always do it later, better to see if you 'like' being a landlord. Sure if the 50K addition will add value for a sale price then it might be worthwhile.
Also a good idea to see if you like living further out, might not work out, but then you can always come back and do the extension. Would it be an idea to rent before buying.
If you do the extension to rent, make sure you borrow the money.