[cflsystems]

css and html knowledge is the absolute minimum to have. to modify templates you need to know smarty

1. You need to modify skin/common_files/mail/html/order_invoice.tpl
2. I am not sure you can distinguish between both
3. You need bots to be able to crawl the site, at least the good bots. That's how your site gets indexed by Google for example. You can restrict bots with robots.txt (not all bots respect it though)
4. You can change what info customer is required to fill out during registration from admin settings user profiles
5. There is a huge amount of free help here in the forum but not everything can be just explained and if anyone works on your site they deserve to get paid