I buy my chicks from local feed stores. I am willing to pay extra to avoid dealing with shipping and possible DOAs, and I want to see the chicks in person so I can reject any that don't look right or that I think could possibly be male.
Same with supplies, most come from the local feed store. I DIY some stuff myself, i.e. a mama heating pad. Chicks really don't need as much stuff as people think, like I raised my first chicks with paper plates for their feeder.
The best auto door is the one that works for your set up. Due to limited space I couldn't have a door that swung out or slid horizontally, so I had to go with guillotine style. Due to frequent very overcast days and wanting to keep birds in past sunrise I opted for timer instead of light sensor, etc. I don't have power run to the coop so I had to do battery. In the end I got a standard Chicken Guard door.