All the features you mention should be part of a plugin, not a theme IMO
yes that would work, the query does’t take into account the product publishing date
yes you can use the “Best Selling Products” shortcode and filter the query using the woocommerce_shortcode_products_query hook.
Congrats, I wish you a bunch of sales!
You should have a look at this post: http://develop.woothemes.com/woocommerce/2014/02/solving-common-issues-after-updating-to-woocommerce-2-1/
Hey, i compiled a list of useful posts about WC 2.1 update: http://www.remicorson.com/woocommerce-2-1-is-out-so-what-now/
All WooThemes premium extensions were tested and updated to work with WC 2.1.
if one your customer already has a PP account, he will be asked to use it (a login form will be displayed based on PP cookies), otherwise, your customer will see a more complete form to enter his personal info and credit card number.