Switching from iOS

Hey guys! So, I have an iPhone 4, and I'm considering switching to a 820 (I don't have a large budget, so), and I was wondering how is the WP world right now.

I had a 710 for a year until the dark ages for 7.x came. I was really into the platform, but the things that were making me furious were:

  • The apps quality. Not the amount of apps, everything I want Windows Phone has, but the apps were poorly built at the time (2012).
  • Notifications. Ok, I know, no notification center, but I just couldn't get notifications. My whatsapp messages, my facebook notifications, and some others, I just wouldn't get notifications.
  • Facebook Messenger. Can I get reliable notifications for the Messenger? Via the messaging app of facebook app? What if I'm not connected, when I connect to wifi, will I receive and get notifications for those messages?
  • Multitasking. Is it really fixed? Using the facebook app in 7.x was just sad, the app would refresh a lot, and would take time to refresh.

I think these are my biggest concerns, and I would love to hear what you guys have to say about them before I jump into the platform again!