How do I know if I am good enough?

That may ruin your job, but it shouldn't ruin your career.

"ecommerce" is a fairly broad term. If you're referring specifically to web retail, I can make a few comments here.

First, the problems to be solved in web retail aren't particularly "hard" in comparison to the kind of problems being solved by, say, the more recent YC startups.

One thing that is critical in web retail is good architecture and clean code, specifically with interface coupling. Between third party order/product feed integration, promotions, special offers, sales tax, duties, shipping concerns, etc, the "special case" and edge condition pile grows very rapidly in this industry. Building a sufficiently generic framework for your system and keeping concerns as loosely coupled as possible is probably the most critical aspect to the technology of a web retailer.

Here are a couple characteristics of the elite in a field (certainly exceptions exist). 1) they know that they are decent to the point that they no longer need peer approval and 2) they have a better understanding of how vast the ‘knowing what you don’t know’ really is. This can create interesting situations in which the best in a field will be the first to tell that they don’t know. I think you are getting to a good place since you realize that there is quite a bit left to learn.

Perhaps instead of thinking: ‘Am I good enough’ think of it as ‘How can I improve’. The idea is to shift the focus toward being your best, which is largely under your control while how hard other people work is not. Those that are internally driven tend to do better since they are trying to maximize their situation. By helping your friends in order to improve your skill set it seems you are doing just that.

You're good enough if they pay you without complaint.

Here's a hopefully useful anecdote from the early 2000's. I had a friend who had worked as a secretary for a few years while getting her BA in Business. Along the way, she somehow took a single class in Statistics that involved learning to program the SAS statistical analysis package.

On the strength of that one class, that wasn't even a programming class, she found a contractor job programming in SAS paying $45/hour which for a former secretary was a fortune. She asked me the same question and I gave the same answer: "if they'll pay you, then you're good enough." And from that week onwards, she happily deposited the paychecks! She confided in me that she felt guilty because she barely had a clue what she was doing and "was taking their money to learn on the job." Welcome to software development! Felt guilty enough to tell her boss who just shushed her with "oh, we know you don't know much; you'll learn."

If you think you can do the job, then apply for it.

You're good enough when you do, do, and do some more and aren't sitting around wondering if you're good enough.

In other words: you're good enough, now get busy.