Some Clarification from OS X users

I have some questions regarding OS X because i want to switch from windows desktop (to iMac) ,I am aware of iMac Refresh and waiting eagerly for it to happen soon , but my decision depends on the answers for some of the questions i have.

1.How does OS X feels ? (is it polished or still needs improvement ?) and How do updates effect OS X ? Updates makes the Macs slow and unstable or they actually improve performance ?

2.Is it painful when Macs gets repair ? Does it cost too much if i get trouble when mac is out of warranty ?

3.How is Mac App Store ? I am big fan of iOS's Appstore , it has great apps and polished experience compared to other platforms , will i find Mac App Store bad ? and what is common cost of each App ? (for example , most common cost in appstore is 99 cents for iPhone and 2.99 for iPad) , and will i be able to re download apps for free if i ever delete an app like in iOS ?

4.How does Windows run on Mac if i ever need it running ?

5.My needs/My content are/is :

-Smooth and Consistent System , With better security and stability (I heard last year so many macs getting infected through an E-Mail and malware)

-Large collection of Photos and also bit photo touching

-managing a big iTunes Library

-Casual Gaming like Chess,Bejewelled etc.

-Browsing/Mails/Video Calls etc.

6.How much speed (minimum) of connection do i need for Airplay to be smooth for any device ?

I am also expecting better integration with my iOS Devices.