Second, no you will not have to repurchase your music. You might have some problems if you music has DRM. In which case you need to get the DRM off. These are the formats supported. You can see several audio formats there, the most common being mp3 files. It does support non-DRM AAC. iTunes has been offering non-DRM'd music for awhile now so how much work you have to do will be dependent on what and when you bought it.
You would have a couple of different options. There are some android apps which can help you move from iTunes to Android. I can't remember the name of it but periodically Amazon offers one as it's daily free App. I expect them to keep doing that.
Personally I've been on a mission for about the past year to un-DRM everything our family owns, convert it to standard mp3 files and get all the metadata corrected and then organized onto a network drive because I'm tired of being device dependent.
Last summer I started uploading all of it to the Amazon Cloud so it will be available for streaming. I'm maybe about 30% done and already I've found so many albums that we've bought two or three times in various formats it isn't even funny. Note, iTunes is moving to a similar Cloud environment but the details on that experience haven't really come to light yet.
In a customer friendly world we'd be able to stream from Apple iCloud to an Android device and from the Amazon Cloud to our Apple Devices but customer friendly isn't always the name of the game.
I have a program at home...(I'd have to look when I get home to see what it's called) that I run every song we buy through iTunes through and convert them to MP3s on the day we buy them.
If you did that, you could put all music on there that has already been purchased.