I am planning on using Google to download the jQuery lib for both UI and Core. My question is, do they allow me to download the CSS for it or should I have to host it myself?
Also if I use Google to load how should I load other plugins? Can I compress all plugins together or should it be its own separate file?
The Google AJAX Libraries API, which includes jQuery UI (currently v1.10.3), also includes popular themes as per the jQuery UI blog:
Google Ajax Libraries API (CDN)
Uncompressed: http://ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.js
Compressed: http://ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.min.js
Themes Uncompressed: black-tie, blitzer, cupertino, dark-hive, dot-luv, eggplant, excite-bike, flick, hot-sneaks, humanity, le-frog, mint-choc, overcast,pepper-grinder, redmond, smoothness, south-street, start, sunny, swanky-purse, trontastic, ui-darkness, ui-lightness, and vader.
Themes Compressed: black-tie, blitzer, cupertino, dark-hive, dot-luv, eggplant, excite-bike, flick, hot-sneaks, humanity, le-frog, mint-choc, overcast,pepper-grinder, redmond, smoothness, south-street, start, sunny, swanky-purse, trontastic, ui-darkness, ui-lightness, and vader.