Ok now that I have a better idea of what you have going on water in about 24 hrs. It looks like you already have some nutrient burn starting on one of your plants
For that size tent the combo you ordered should work well to keep your temps in check and create better air flow. In the future you could always add an inline fan to help it out if needed
Allow another 2 or 3 days before you water. Before you water the plants lift the pots and get a feel for the weight. water until you get 10-20% run off then lift the pots again. That will give you a better idea when to water next time
He means water the least often you can. Allow the soil to completely dry before next watering, you should be doing that regardless so your roots search for water and create at nice root structure
Yellowing cotyledons is normal. Your pots are way to small, could be a root issue?
Anyways with autos you should plant them directly into the pot they will be finishing in(3-5gallon pots are a good choice)
Most soils have time released nutrients so washing them out isn't really possible. As the poster above said, you can add perlite peat or another neutral soil additive to make the soil less nutrient rich.