Ok, all seeds germinated today, and i put them in soil, made the closet setup, now im waiting for babys to come out

im very interesed in keeping the plants small, i dont want them to grow tall, please give ur suggestion what/how to do.

what temperature should be in the closet? say in Celsius please

the soil pH nivel is: 5.5-6, what pH plants need to grow good?

here are some pics: