the suction cup most likely won't seal. you can take a very fine tip flat head precision screwdriver and wedge it between the rubber gasket and the metal bezel down by the home button. pry up gently, try not to damage the gasket. also be careful of the electronics on the dock assembly and the home button ribbon.
try putting it into recovery mode. the phone needs to be off. have itunes open on your computer and the cable plugged into the computer but not the phone. with the phone off, hold the home button for 10 seconds then plug the cable into the phone. see if the computer recognizes it after that. putting it in recovery mode will force you to restore the phone so you will lose anything you had on it.
it could be a bad lcd chip on the logic board. it happens a lot with liquid damaged phones. if a new lcd does not work then i would believe the chip would need to be replaced. no guarantee. it's extremely difficult to solder something that small, but we're champs at it here.
that's a tough one.. the only way to get that new volume button in there is to remove the bezel from the back palstic part. which i don't recomment trying because it's glued together. you will have to disassemble the whole phone separate the bezel from the plastic and use super glue to get it back together. it might be easier to buy a complete back housing with the bezel, back housing and volume button already together. but that still involves you disassembling your whole phone and building it in the new piece. matt