Tomatillos have perfect flowers and are technically self-fertile however they are very poor at self-pollination. Hence the suggestions to have 2 different plants. Or you can hand pollinate if you don't have room for two.

Not sure about the pollination, since I generally grow several plants. I seem to remember growing a single purple tomatillo in the 1990's, and getting fruit.

Perhaps the most important things to know about starting tomatillos is that they grow faster than tomatoes, and quickly become leggy. I plant them 2-3 weeks later than tomatoes. They are also very intolerant of being left in pots too long, and may yellow & die. If the plants become tall & start to yellow, you can cut off the top, and root it in water. That cutting might survive if the mother plant dies... and if both survive, you have plants to give away. :-)

Tomatillos are temperamental transplants, and it is not unusual for the plants to die in the pot - especially if grown under lights. It is good practice to start a second set a couple weeks later than the first, as insurance.

In my experience, tomatillo plants are much weedier and weaker/spindlier than tomato plants, so I think you’ll have room for two. I squeeze a few plants in somewhere after all the other planting is done. I’ve never had transplant problems. They don’t even mind a little light shade. I’m in z5, growing them in sandy soil… mature plants usually handle light frosts well here too! and tomatillos are long keepers in cool storage.

Maybe a little late for lolear but what I've done in the past is start 2-3 seedlings in the same container. Takes up about the same space in the garden as one plant.