Do I put vinegar in the water when poaching an egg?
By far the most important factor in a nice poached egg is the freshness of the egg.

Fresh eggs shouldn't need vinegar to help them set, but It can help with an older egg, whose white has started to go a bit runnier. Vinegar does leave a flavor, but if you're poaching your eggs ahead of time and putting them in iced water to stop them cooking, that does seem to wash it out.

Salting the water will toughen an egg, better to season it after it comes out.

A large egg, starting at room temperature, in barely simmering water (trembling) will take 3 1/2 minutes to just solidify the white, and leave the yolk very fluid. If you want your yolk more viscous, another half minute.