Yes, you develop all of these just with Notepad++ (the way professionals do). Add to that a good experience in Photoshop for the graphics, and a good knowledge of marketing (bad marketing with beautiful graphics leads to no-sales!)
Many people start downloading pre-written code like os-commerce, a free open-source e-commerce, and try to adapt it to their needs: this is a daunting task, as the user does NOT understand the code he is using!
As for payment gateway, yes, PayPal is the easiest (and fastest, and cheapest) of all banking gateways, IF you are using simple transaction system (just a few kb of code). If you try to implement your shopping cart IN PayPal, you are in again for a very hard time if you are not fully conversant in programming. Personally, I develop my own shopping carts, and end-up with ONE transaction through PayPal. Simple and easy.
Finally: security. If you use a one-off call to paypal, you do not need any security: let PayPal do it for you! This means, of course, that you do NOT collect any private information from your clients, save their names and addresses. NO credit card info, EVER! If you do so, you must set-up your server with SSL, buy and maintain a security certificate... a real pain.
To conclude: since you say you do not have the time to learn, go to professionals: there are enough freelancers about, that can provide you with good service for a reasonnable price.
I develop full e-commerce and complex applications, but my fee starts at 4500us$. However, at www.rentacoder.com, you may find developers that will offer you e-commerce for around 1500us$.
BEWARE of lower offers: you'll NEVER get your site of the ground (these are amateur's offers who have no idea in what is involved!)
Best of luck!
Pro web2 application developer at www.web2coders.com