Sandeep Hello,
Let's take one thing at a time.
When you sign up for a merchant account to process Visa/MC, you typically need 2 additional components to make your online store work. 1. A payment gateway - which acts as a virtual terminal. Verisign and Authorize.net are the key players. 2. A shopping cart. There are literally thousands to choose from - from beginner level to advanced. Usually, your merchant processor will give you a free beginner level shopping cart package.
Security is a complex issue. What type of concerns do you have have about processing online?
Logistics. Do you plan on shipping worldwide, or domestically? What courier do you plan on using? In the USA, UPS, USPS, FedEx and Airborne all make it very easy to integrate into online stores. I know that UPS in USA will send out a techie at no charge if you are having trouble integrating their WorldShip software with the back end of your site.
In the future, try not to clump all your questions in 1 single post. It makes it hard to follow.