I've read a lot of advice about when to water seedlings, but apparently I'm still overwatering (see this post and this post). So, I thought I'd ask you folks and see if you can help me figure out where I'm going wrong.

The most basic question: how do you know when a plant needs water? I have many seedlings (~100), and they all dry out at different rates. What's the best way to check each one quickly, so I can only water the ones that need it?

For instance, do you wait for a plant to wilt slightly, or is it bad for a seedling to get very dry before watering?

Or, does anyone use a moisture meter? (I find that sticking my finger in the soil may work for larger pots, but for small seedlings it's more difficult because there's less room to do so without damaging the plant or its roots.)

When I water, how much should I water? Should I water until it runs out the bottom, or should I try to water less so that the soil doesn't get so saturated? (The pots have good drainage but it can still get quite wet if I water until it drains out the bottom.)

I very much appreciate any help people can give!