MacBook – Connect 2 external monitors with MacBook Pro

Here's one example of someone running two 27" displays at 2560x1440 via Thunderbolt/DisplayPort plus an HDMI display at 1920x1200: http://blog.macsales.com/14241-macbook-pro-15-with-retina-display-can-run-3-external-displays

The Thunderbolt ports officially support up to 2560x1600 so that resolution shouldn't be any problem either:

Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on up to two external displays, at millions of colors http://www.apple.com/macbook-pro/specs/

To get up to that resolution, you're limited to either Thunderbolt/MiniDisplayPort or Dual-Link DVI via an adapter - single link DVI and VGA adapters won't go that high.

For the HDMI port, I haven't seen any specific maximum resolution. This person got up to 2048x1280: http://reviews.cnet.com/8301-3121_7-57460642-220/how-to-power-four-simultaneous-screens-with-the-retina-macbook-pro/

Generally, external monitors work fine in Windows. I see no reason why it would be any different on the Retina model or on Windows 8 specifically.

Yes, you will get 1920x1080 resolution.

The native resolution of a 13" Retina Macbook Pro is actually much higher. From Apples website:

Retina display: 13.3-inch (diagonal) LED-backlit display with IPS technology; 2560-by-1600 resolution at 227 pixels per inch with support for millions of colors

Native resolution: 2560 by 1600 pixels (Retina); scaled resolutions: 1680 by 1050, 1440 by 900, and 1024 by 640 pixels

The 13" retina MBP can also handle 1080P and higher resolutions through HDMI:

HDMI video output

Support for 1080p resolution at up to 60Hz

Support for 3840-by-2160 resolution at 30Hz

Support for 4096-by-2160 resolution at 24Hz

http://www.apple.com/macbook-pro/specs-retina/