I say use whatever you have easy access to and get started. I know too many people that held off on painting because they worried about having the right paint, the right brush, the right medium, the right whatever. It's art. There is no consistently right way to art although there are correct ways to do techniques which is what most painting advice covers. I still use craft paints from time to time and mix them with my hobby paints. GW, Vallejo, P3, Army Painter, and Reaper are all fine brands. I would pick one where you can buy local if you want just one brand because you never know when you might get the itch to paint something and have trouble mixing the exact colour you want. All of those brands mix with each other so which of those brands you buy to start is not all that important, but I understand the urge to not have to learn the properties of different paint lines to start.. If you buy a spray primer then make certain it is primer and not spray paint. I know Walmart brand only comes in grae, but it will be sitting next to flat black and flat white paint so it is easy to think they are primers as well. I feel the best things to focus on to start are simply getting paint on the model and mixing some of your own colours.