Weddings are no easy task, but given the situation I can understand them asking you and you saying yes. The answers I'll give to your questions are not really
great advice, just safe ideas that will get you through the day. If you were asking about starting up a wedding photogrpahy business on the side then the answers I would give would be completely different.
1) Most weddings photographers I've worked with (I'm a professional wedding videographer) use a 24-70 & a 70-200 f/2.8 on a full frame camera. If you're able to rent it, the 16-50 as mentioned before is a good choice. You're going to need something a bit longer than the kit lens during the ceremony, as you won't want to be right in their faces the whole time.
2) Get a flash. Something like the Sigma EF-530 DG ST which is cheap and versatile. It will let you bounce off ceilings indoors and fill in shadows outdoors for good (though not amazing, when used on camera) portraits and group shots. A flash will give you more chances to get photos because you'll be able to shoot from any direction regardless of where the sun is. And it will let you set up group shots with the subjects backlit and the flash filling in to get nice, quick, results without too much fuss.
3) It's a bit late at this stage for books, but try the internet.
4) I find there's not a lot of wedding photography/videopgrahy tips or tutorials on the internet, mainly because most people don't want to give away their secrets for free. However, you'll have good results if you type in a google search for something like "photo portait tips" or "indoor photo tips" and then apply those to your situation. Look for tutorials or tips that use minimal equipment.
5) Other tips - shoot in AV mode - let the camera do some of the decision making for you so you can focus more on what is happening around you. Shoot RAW so you can recover some of your exposure mistakes later on. Try to visit the locations in advance so you know what you're dealing with. Bring lots of batteries and cards. Stick to the basics - rule of thirds, leading diagonals, etc. Print out a good posing guide to carry with you so you are never short of ideas. this one here has some good ones for males, females and couples -
Lynn Herrick Photography - Posing Guide - I suggest you cut out the ones you like and paste them onto a single A4 page to carry with you. Be friendly with all the guests - smile, joke, compliment them - and they will be more relaxed in front of the camera. Make sure you can carry everything in one bag - you're going to need to move quickly and can't stop to pick things up or shuffle gear around. When indoors, (unless the roof is super high such as in a church) bounce flash off the ceiling and when outside, shoot towards the sun and use fill flash - these techniques are a quick way of putting more depth in your photos and will noticiably seperate your work from the billions of standard 'facebook snaps' people take at these sorts of events.
Also have a chat with the bride/groom/family beforehand and let them know that you will do your best but you can't promise you'll deliver professional results. You have limited equipment, experience and time to prepare, so make sure they understand that so you don't end up with any dissapointment or tension later on. Then they'll be pleasntly surprised later on when you deliver some really nice shots!