I have been trying

I have been trying to customize the themes. I do not see any easy or difficult way to do it. Very frustrated. Here is what I am trying:

Change the Colors
Change the First Page
Change the Menu
Add Widgets to the Header and Footer and Side Bar
I am trying to integrate Marketpress and looks like subscribing to your monthly membership messed all the links. I am getting 404 on product categories.

Did I just ruin a wordpress site?
Please help.