I cannot afford a barbell, and all the various weight plates that would need to go with it. Therefore, for the exercises that use a barbell, is it just as good to use dumbbells instead?
Yep. I use dumbbells all the time and actually like them better. The only exercise that I find difficult to sub is the squat, because in order to keep proper form, you have to hold the dumbbells up. You can probably rest them on your shoulders, but the barbell is more comfortable.
Me too - I just don't want to take up the space with a barbell and various plates so I just use dumb bells. Just be prepared that setting higher weight db's on your shoulders is not comfortable - but for me it's a trade off I can live with!