When my flowers start to grow and mature, is it necessary to keep them under lights still or will a south facing sunny window be enough? Thanks!
A window sill especially if it's south facing will give a plant some light but it is not ideal. It is mostly reflected light. You have eaves that stop any direct light so they will only get direct light if the sun is below thw eaves and that won't be long.
If these are flowers you plan on planting outside then keep them under the lights or put them outside in a protected place in the day and bring them in at night. Do this AFTER you harden them off
Sun is necessary. Growing herbs indoors want a very sunny south-facing windowsill, and even so you likely won't get as flourishing a harvest as you would outdoors. Many flowers need that they will need a place where the sun shines at least eight hours a day.