dabac

OWell, we learn from our challenges.
No trueing stand does that. "Completely" true depends A LOT more on the guy doing the work and the condition of the rim to start with. To true a wheel you need a way to spin it, and something to act as a reference point. Trueing stands does this easier, slicker. But not much principally better. At least not until you get into the realm of dial gauges...
Kinda-sorta. While brake rub certainly can be quite annoying, it takes a fair amount of untrue before the actual brake drag becomes an immediate problem while riding. What ALSO happens with an untrue wheel is that your contact patch no longer follow a straight line. The wheel will start to shift sideways and back on each rotation. Quite annoying and outright dangerous when you get up to speed.
Again, the quality of the true is far more dependent on the person doing the work than what equipment is being used. Trueing stands mostly make the work faster and more comfortable.
Also, be wary of the phrase "completely true".
First off, there's no such thing. That's all down to how accurately you intend to measure them.
Next, we don't need it. We ride on randomly uneven surfaces, on air-filled tires with their own deviations from round and true. Better than "good enough" will bring no noticeable improvement.
Third, sometimes it's not even desirable. Few rims are exactly round and true even at the start. Often wheel work ends up at a compromise between true, round and spoke tension. And sacrificing a good spoke tension balance on the altar of trueness is rarely a good idea.
Put a zip tie around each fork leg or chain stay. Firmly but not full-on tight. Cut slightly longer than neede for the tip to reach the rim. Rotate the tie around the stay/fork leg to increase or decrease clearance.
Easier to see than brake pad clearance. Dirt cheap. No storage issues. Good for sub-millimeter accuracy, if you think you need it and have the patience.