just use the 400....u don't need a special light for seedlings, just keep a good distance at first.some folk use 1000w from start to finish and some use the sun.
heat to 100f in the morning, wrap with hot hands packet (rubber bands work well) and ball it. make sure you are dressed warm if it's cold out....like insulated underwear n all. it should stay above 96f for quite a few hours.
after you pass order the plastic bottle with temp gauge on em. good...
having to trim all that by hand could be stressful...lol
i find it calming myself, although when i get an issue i can't get a handle on i do get some what stressed.