Oxygen Theme Description http://theme.wordpress.com/themes/oxygen/ Live demo site http://oxygendemo.wordpress.com/
In Oxygen you can either have a Home page that displays your posts or a static front page ie. a Showcase template. http://en.support.wordpress.com/pages/front-page/#setting-up-a-static-front-page
Showcase page template
When you first activate Oxygen, you’ll see your posts in a traditional blog format but if you’d like to showcase your content in an online magazine-like fashion, then you can use the Showcase Page template. ...
Sticky post thumbnails are 750 pixels wide in the featured slider
Regular post thumbnails are 450 pixels wide
If you don't see the page attributes module then make sure that you don't have it hidden in your screen options http://en.support.wordpress.com/screen-options/
Modules to unhide:
Post – Likes and Shares, Format*, Categories, Tags, Excerpt, Send Trackbacks, Discussion, Comments**, Slug, Author, Revisions, Writing Helper
Page – Likes and Shares, Page Attributes, Featured Image, Discussion, Comments**, Page Revisions, Slug, Author, Revisions, Writing Helper
Please be aware that you cannot crop the sticky post thumbnails.