Would my printer work with it, for example? Yes
Would the specifications be as good, for a similar price? Generally, laptops are slightly more expensive for a similar spec.
Where would I sell my "old" PC, if I bought the laptop? Your local rag or Computer shop? But don't expect to get too much for it and make sure you format the HDD before selling it.
Where's the best place to buy a laptop? Not the cheapest - but well made and robust. I wouldn't use anybody else click here
Are laptops as reliable and easy to fix? Reliable - yes. Easy to fix - no, because the components are smaller and more complex and usually have to be replaced en masse rather than individually as in a desktop.