The best way to test this is to use the voice recorder app and make sure that the "speaker" button in the top left corner of the screen isn't enabled - this means that the sound recording will play through the ear speaker.
If you can't hear anything then make sure that ribbon cable number 3 is fully pushed in, I like to use a pair of tweezers to help me and then the blue opening tool to flip down the clamp on the logic board. If you still can't hear anything then you may have a faulty part, if you bought from eBay they should sent you another without a problem - in the UK I pay £15 for the whole mid-frame, ear speaker and home button and I have never had any problems in this price range! I think that's around $20
As for the screen brightness you could try using another LCD to see if you get the same problem. If you do you might have a bent pin on the logic board which requires a difficult repair.