If you’d like to save space, you may also want some smaller cell trays - I like these sturdy 72 cell plug flats - for cool season seedlings, like lettuce and kale, that only need to be indoors for three to four weeks.
The sizes you will need depend on what you want to grow and how long they will need to be indoors before transplanting. The 6 cell packs are the most versatile for a minimal setup, most seeds can be started in them. If you are starting certain warm-season seedlings, like tomatoes or peppers, that grow indoors anywhere from six to 12 weeks, you will also need larger containers to pot them up into when they grow too big for the 6 packs. Three - four inch pots, or large plastic or Styrofoam cups work well for this. If you’d like to save space, you may also want some smaller cell trays - I like these sturdy 72 cell plug flats - for cool season seedlings, like lettuce and kale, that only need to be indoors for three to four weeks.