It's not a bad idea to dilute your FFOF soil as it does contain all the nutrients plants need for a full life cycle already. You can add whatever to lighten it up especially perlite as it is a bit heavy. I've never had a problem with putting seedlings right in it- organic based nutrients are...
To make it ez on yourself I recommend using a premixed and ph balanced soil like Fox farms ocean forest or equivalent. Then all you need to add is 20% perlite and set a watering schedule. To start your seeds use damp rockwool cubes sealed in a ziplock bag stored at room temp or a bit warmer for...
Staggering plants requires precise timing and it helps to have a separate veg & flower area for this. Just a few suggestions to help you:
1) I find that as a general rule you want a bare minimum of 100w per plant.. Your 400w will just barely meet the needs of 4 flowering plants; doable but...
Don't buy crap to cover up the smell... Vent out your grow room or tent with an inline fan connected with dryer ducts and a charcoal filter. Got a 240 cfm inline fan for $30 and the filter for $60....rank odors eliminated instantly