OK, I build wheels but even if I wasn't i would absolutely have a spoke tension gauge. There is no way plucking spokes tells you much of anything and absolutely does not tell you what the tension is...and that matters. The park gauge, and probably others come with a chart that tells you what the actual tension is and it's easy enough to find out proper tensions for the rims. Soft wheels break spokes and I know from personal experience "bought" wheels can be really off
In addition to that it's nice to have some sort of truing stand, even if you make it out of a dumpster bike. It's a lot easier than doing it on the bike. You can determine if the dish is OK just by flipping the wheel in your "stand"