Growing your own food? Welcome to the dark side.
You have a lot of learning to do :)
Yes, you will want to keep track of your greenhouse temps and for sure
keep the door open on sunny days, and even days that are calm and
overcast. Put a thermometer in there and you'll be surprised at how
high the temps can go! One afternoon without cracking the vent can
cook all your seedlings into soup.
Having said that, make sure your GH is secured so a stiff breeze
doesn't carry it off. Tie it down with whatever!
Google this group for seed starting advice - lots of folks have been
down the road you are just starting on. There will be conflicting
advice but if you are truly concerned then don't put all your seeds
into one method, try a couple on for size and see what works for you.
You will not need to feed seedlings until after they develop their
true leaves. Seeds contain all the nutrition they need esp. at
first! True leaf-stage is when you can think about potting on your
seedlings to larger containers. I fertilize with a WEAK mix at this
stage, give them a day in the dark to recover, then feed again when
planting out. Some plants want a side dressing when they begin to
Sprays come out when I can't stand the pests anymore - but that's
indiscriminate, and likely to hurt the good bugs as well as the bad
bugs. A better choice IMO is exclusion - if you have a crop that bugs
love, put some floating row cover over it and say goodbye to re-
applying every time you water or it rains.
The plants you have seeded in the garden don't get moved. Some plants
will over-winter for you: in Z5, that means onions, spinach, garlic.
First crops of the season are from over-wintered plants for me.
Good luck - do more research! As Mulder might say, the Truth is out
there - waiting for you!