I use my phone for the contacts,and calendar,I sync to computer and if something happens to my phone I can load it right back on. iPhone should do the same I would think. I use Gmail,would I be able to keep using it or have to change it?I've made the switch.
For a long time I have been using windows CE and windows mobile, up to 6.5.
After that I've used a windows phone 7 series, but the lack of apps and progress with the new windows phone 8 made me switch to Android.
In a few weeks time I've used a Samsung S2, a Sony Xperia S and a HTC One X. But Android just wasn't for me, I was constant having that eerie feeling that I'd chosen the wrong product. Constantly trying new launchers and programs that I needed for productivity, never found a good match.
Out of sheer frustration I bought a new 4s and never looked back, not at Android or wp.
I heard you on the back up of a back up.Yes, the iPhone does that and then some.
However I would suggest you move your calendar and contacts to iCloud when you buy your iPhone. Google is dropping support for EAS (Exchange ActiveSync). While they (Google) say that they will continue EAS for existing connections I wonder for how long. You can leave a copy of you contacts in gmail for access via gmail.com if you like. Only caveat would be if you are sharing your google calendar with another person, I have yet to find a way to share my iCloud calendar to a non-Apple user.
Moving your data over would be quite simple while Google still supports export .vcards and .ics (contacts and calendar exports).
Also moving your data into iCloud would eliminate the need for a physical backup on your computer as it supports backups of your data and settings to iCloud. But it's never a bad idea to have a backup of a backup