A variable total order discount ... and also how to change prices en masse

Hi, I have 2 questions:

1. I'd like to know how I can setup a variable total order discount if possible? Let me explain...

I want to offer my customers a different total discounts, based on total order amount. For example:

if total order is > 50$ discount is 5% so the charge is 47,5$
if total order is > 100$ discount is 8%
if total order is > 130$ discount is 10% etc... etc...

2. CAn I perform a bulk price change to a selected category or subcutegory of products? For example I want all products in category SHOES to raise for 10%, but I do not want old price to be displayed as strikethrough.

I'd start with dreamscapes Global Quantity Discount orders total module and adapt it based on the scale you have established ...