Hey Mike! Man you're going to have fun. I'm thinking about grabbing that kit as well. Please give us a play by play and let us know how everything performs. I'm a new brewer as well so i'm trying to tread lightly.
Airlock Q: Yep fill with sanitizer. Do whatever you can do to clean them. There's alot of cleaners out there that can get crap out of tight spaces... plus you can always pressure hose them out with whatever means, then sanitize. In the end though, those airlocks are a buck-fiddy each at your local/favorite homebrew store so if one gets too caked up and uncleanable you arent out too much to replace it.
Hydrometer Q: This site has an AWESOME wiki. Here's the hydrometer wiki:
http://www.homebrewtalk.com/wiki/index.php/Hydrometer I'd suggest using it in a beer or something instead of plain tap water... sanitize everything first and you can still drink the beer afterward :P
Ingredient Storage Q: <snip> Edit: they already answered ya there so i'll just take that out.
Again, welcome to the forum and let us know how it goes!