Speaker / Head Unit Question (2011 1.8S 4D Hatch)

Hey gang, brand new here and wanted to say hello.

I had a couple questions hopefully you guys could answer, I've searched what I could but most of the threads are of a different year or make, and I want to be sure before moving forward.

So anyway, I am curious about which speaker size will fit the 4 mounts currently on the car? I would like to replace the 2 front and 2 rear, and I've been looking on amazon for 6.5"W x 2.5"D - does this sound like it would fit? Here's an example:

Amazon.com: Infinity Reference 6032cf 6.5-Inch 180-Watt High-Performance Two-Way Speakers (Pair): Electronics

(The product dimensions here read 10 x 5 x 5 inches, but the item name is obviously 6.5 inch speakers). Does the 10x5x5 refer to packaging dimensions or am I totally missing something?

I always would like to replace the head unit, I don't need much help with that, but wondered if you guys had any recommendations for the $100-$150 range. I'd like good low-end, doesn't need to be gut busting though. For that matter, any speakers also recommended in the $60/pair range?

The last thing I wanted to ask about we're the door panels, I've done a head unit and speakers on a '91 jetta and '92 jeep, but haven't messed with the electrical on a newer car. Do these panels just pull off? Release tabs or buttons anywhere? Or anything I should watch out for?

Thanks for reading, I appreciate anyone who is willing to help out!