For the keyboard backlight:
Have you tried pressing the "lights on" F-key, that has like a half-round rays of light over a bar symbol (currently F6 on my Mac, but may be different on other models)? If it doesn't work, does anything show on the screen?
If a crossed-out symbol pops up onscreen when you press the F-key, that means that automatic keyboard lighting is enabled and the Mac thinks surroundings are too bright already. Go to System Preferences / Keyboard and uncheck the "Automatically illuminate keyboard..." item, then try again.
For the screws:
Visit www.powerbookmedic.com or www.ifixit.com and see in their Mac parts section for a replacement screw set. You will need to know your Mac's model, printed on the bottom lid, to ensure you get the correct parts for that particular computer.
For the RAM:
While in either of the two places I mentioned above, visit their How-To / DIY section for instructions on how to replace RAM on your Mac. Then visit www.crucial.com, www.corsair.com, www.kingston.com, www.otherworldcomputing.com or any other RAM maker, use their RAM advisor together with your Mac's model to select the correct RAM upgrade kit for your Mac.