Let me explain some fundamentals which are imperative to understand how this works.
The Ego center which is the heart center ( energy centers - derived from the Hindu Brahmin chakra system) is a center that operates on a frequency that we feel/communicate as Will power. This is the center that corroborates with self esteem, courage and sense of self worth. It is also a motor. Meaning it is a center that has a mechanism that drives for action. In a simplified language, you can summon your will power to do something that is awfully difficult or undesirable.
The second thing is that if you draw a map of all the energy centers that are in a human, the ego center is right there in each one of us. However there is a binary there. That center ( as any other) can either be defined or undefined (open)
70% of the population has this center undefined. And that translates as chemistry in them that: they are not good enough, that they don't have will power, that they lack courage, that they are not worthy for whatever, that they cannot sustain commitments.
Please note that defined or undefined does not mean good or bad. It's just is.
So now to your questions.
How do I know if I have an ego?
You have an ego center. Whether it's defined or not that is the real question.
Is an ego bad? Ego is not a bad thing. Without the ego center you're dead.
How much ego is healthy? The reality is that ego had gotten such a bad reputation over the years. But it's very clear to me that it derives from all those people who have it undefined. They are constantly trying to prove themselves worthy and this leads to distortion in this frequency field which translates to what we call narcissistic, egotistic behavior.
Remember that what appears to be on the surface is very different to almost the exact opposite than the motivation behind it.
How to develop ego? That's a typical mind question and I don't mean to be rude.
You can't develop ego.
Either you have it defined which means you have that energy in a consistent manner. It's there 24/7 all the time till the day you leave this plane or it is undefined and you have bouts of it depending on the people that are around you. If you understand the mechanics you can become free of the burden of your mind interjecting that you must “do” this or that to change or develop or stop or whatever for a desired outcome.