First of all, welcome to Platinax.
The first thing that comes across is that you're eager to sell online, but you've got problems determining which industry you really want to target.
This could be crucial - PC hardware has a reputation for low-margins, and the mobile phone market is certainly competitive. Selling coffee online could be a good niche market to sell to, but how much understanding of the marketplace for this do you have?
I guess in that instance, you really need to weigh up what you know about each industry, and how you think you'll be able to target it profitably, espcially with long term goals in mind.
Once you have a basic idea of that, you can at least develop some form of business plan, to gauge your options perhaps a little more clearly.
Certainly there are a number of technical considerations to bear in mind when selling online - how much do you feel you understand this aspect? This could be especially crucial, as knowing how to reach out and market to customers, let alone process transactions, could be key areas you'll need to understand.
Hopefully more detailed questions will receive more detailed answers.