Plumbing – Bizarre cold water bypass

I'm not a professional plumber (though I did work on water treatment systems for several years), but in my opinion what you did is fine.

Gate and globe (stop) valves are prone to corrosion and generally wear out over time. Ball valves are much more durable and reliable. I've seen many, many old stop valves that are leaking or don't shut off properly, or more often, leak as soon as you open/close them after they've not been touched for years. I can't say the same for ball valves - I've seen many that were installed for many years and still worked. I can even think of a couple where the outside looked totally corroded, and though it took a lot of force to turn (and sometimes a replacement handle), they still reliably shut without leaking.

On top of the reliability, the fact they use a 1/4 turn (instead of several full turns) and a quick glance tells you whether it's open or closed, ball valves are just vastly superior to gate and globe valves for almost all residential applications. Worth the extra dollar or so they cost.

The only thing they are not as good for is applications where you want to limit/control the flow rate (such as an outside tap or sample port). They can still do that, but are harder to finely adjust, and especially when one hasn't been opened for a long time and is a bit stiff, tend to suddenly give and open to full blast (I've been sprayed while trying to take water samples many times).

Hearing a small amount of noise from a water meter vibrating is not uncommon, however if the noise is loud enough to be distracting, you may have a worn impeller in the meter. You can try holding the meter securely or applying some pressure to the meter to see it that reduces the noise, but also you will be able to feel if the vibration is coming from the meter itself. If simply holding the meter or the lines attached reduce the noise to an acceptable level, then securing the pipes to a wall bracket or clamping them securely may be all you need to do. If this test does not lower the noise and you can feel the vibration through the meter housing, then I'd suggest calling your water utility company. They own the meter and would come out to replace it if necessary, usually at no cost to the consumer.