Upcoming Android User - a few questions

Hello! I'm new to the side of the woods, but I am pretty sure that all get the answers I'm looking for with you guys. If there are similar threats to this one, you can just give me the link; I don't want to be one of those annoying users just repeats what's previously been asked. I tried searching little bit but couldn't find a thread that addressed my questions, but if there already is one just let me know! :)

I just moved to France for business school. My iPhone 5 was carrier locked, so I had to leave it behind in my home country and bring my old trusty iPhone 4 with me. Quite frankly, I can't stand it. It is way too slow to be used on iOS 7. prices for electronics are outright insane here, so the iPhone 5s is completely out of my price range. I've been reading about the upcoming Nexus 5, which seems to be a high-end phone with a stock operating system at a reasonable price unlocked. Assuming it really does hit the 300 to 400 (base) price range that has been rumored, it is my next.

Migrating

I use Gmail almost exclusively as my personal email service. I actually have to pay an annual fee because my current inbox is over 23 GB. Despite this, my contact list and calendar on Gmail are completely disorganized. Years of random email addresses are stored there, and there are a lot of instances of duplicate contacts. My iCloud account on the other hand is pristine. Is there anyway for me to import my iCloud contact list into an android phone? That is the single most important step for my initial setup. I saw something about the Moto X having a migration assistant - will this work on a Nexus?

Sync

I read something about drag and drop not working properly on OS X. Is this correct? I have used iTunes as my synchronization suite for years now, and I am willing to accept the learning curve for a new mechanism but I am completely lost in the woods here. What software do you guys use to keep your music synchronized? Things like playlists, play counts, and recent downloads are far easier to manage with software then manually dragging things back-and-forth into folders.

Apps

I know most of the big-name apps are multi platform. Instagram, Pocket, Evernote, Facebook, Whatsapp, Skype, Dropbox, Snapchat, etc. I know will be covered from the get go. But there are a few services I'd like to check: what Twitter application do you guys recommend (I use Tweetbot on iOS)? A "presentation remote" app for clicking through Powerpoints on my Mac? Any Android-exclusive cool apps I should be aware of?

Tweaks

My father is an Android diehard user, actively engaged in the XDA community. He genuinely enjoys messing around with his phone (the way I mess around on my desktop). Having used non-Jailbroken iPhones for quite a while, I've never really felt the urge for it but I know it's one of Android's strengths (flexibility). I consider myself a power user - if there is a compelling enough reason to root and install a custom ROM or firmware or launcher or whatever I am confident I could pull it off after a little reading. Considering I'll be getting a Nexus, is there any particular tweak that you feel is truly great in your personal usage? I'd love to hear about the cool things you guys are doing on Android!

Thanks in advance for your help! If there's any information you feel is relevant despite not being explicitly asked please do share it! It'll be a totally new experience for me.

For the TL;DR crowd: Can I get my iCloud contacts into a Nexus 5? Must-have apps? Any really awesome ROM/launcher/whatever thingy I should look up?

A.