There are two very important aspects of selling online. Of course the first is to generate some sales of your products or those you promote as an affiliate. But the other thing is huge as well. That is your list and how you market to it.
The first two investments people usually make when the decide to sell ebooks online are a domain name and a web hosting account. Those things will establish a presence for you online.
The third investment should probably be an auto-responder service. A good service such as Getresponse or Aweber will only run about $20 a month; It is worth far, far more than that. I personally have used Getresponse for many years so can fully recommend it.
An auto-responder service is much more than a service that lets you send out bulk emails to your list. A good auto-responder service will allow you to create pop-up forms to use in opting in visitors to your list. It should allow you to create multiple, sequential emails to send to your subscribers. This creates an auto-pilot system for marketing to your list.
Of course you can create spontaneous emails and queue them to send at any desired time. Tracking is an important consideration as well. A good auto-responder service will track the open rates of your emails, the percentage of people who are actually clicking on your links in your emails, and bounce rates.
I would also recommend a service that allows you to do split testing of your lists. This is important because as your list grows, you may want to test two versions of an email to see which pulls the most sales.
You should also use a service that allows for the creation of double-opt-in lists. Here, visitors opt-in to your list, but then they are sent an immediate auto-response requesting them to confirm their wish to subscribe to your list. This is almost a must. It prevents people from claiming they never signed up for your list.
As for mailing, everyone has their own schedules. A good schedule is to mail 2-3 times a week, but many top marketers mail every single day to their lists. I consider that a bit much. The important thing is to maintain contact with your subscribers and provide them with valuable information. Build a relationship with them and they will be more likely to do business with you.