How important is the "don't disturb the roots" warning???

Depends on the plant. Most plants, with the exception of those where the root forms the edible portion (ie. carrot, radish) tolerate the root disturbance that comes with potting up and transplanting just fine. In other words the claim isn't all that important.

In the case of your tomatoes the act of potting-up and the normal amount of root disturbance that accompanies it is beneficial. It is the trigger needed to form the fibrous feeder roots. That doesn't mean you can trash and bash them of course but slowly pulling them apart doesn't hurt them.

If by "community germinating containers" you mean don't plant different plants with different germination times in the same container, you are right. If you mean don't plant multiple seeds of the same plant in the same container, then no. Germinating multiple tomato seeds in the same cell or small container is a common industry practice.

Dave

Perfect.

I knew better (thanks to info on here) to do tomatoes with peppers but when I was dividing my Patio Princess and my BushSteak tomatoes, I used a spoon to scoop them out and, inadvertently, had to deal with tangled roots...

Again, thank you.

I will have to wait and see what becomes of what I did! LOL!

Tomatoes are easily manipulated with no harm . I germinate 1 variety per pot and separate them when a inch or so high . I also take cuttings to root when plants are large enough . Pepper cuttings can also be rooted .