I suggest that before you buy a domain,you must think about a business that you want to develop, or where you want to occupy and act accordingly.
Usually this is what a so-called end-user thinks, and many times the difference between domainers and customers is not so far away.
To start making the domainer we must first set a strategy, short, middle or long term and carry it forward with perseverance and passion.
Of course, to find good domains need the experience and also a bit of luck, but really in this world, even the "good domain" may not make a difference, as it could make the poor.
So you see the skills of a domainer can go to a particular skill in marketing, in assessing what can be brandable, excellent programmer who develops and sells.
So I think that first of all you must think about what you want to do in the future then your acquisitions. I would start with just one domain and I would try to see if it does well after development. Set a medium-term strategy for it, and see what and how to improve it.