Need a location first, that way suggestions can be made as to the types of chickens would be best for your area. If you have a hard winter, then you would need to look at cold hearty birds. Do you just want egg chickens, are they going to be able to free range or will they be kept in a run.
Do you want to raise them from chicks or were you looking at pullets at POL. If you go towards chicks, you are looking at a minimum of 5 months before you will see any eggs. Also with chicks, they will needs to be kept in the brooder till they feather out & the weather is good (day & night) before they should be put in the coop. If you are looking at pullets, make sure the person you buy them from have healthy birds.
Build the coop & run first, and build it bigger than you think you want it. Make sure you use hardware cloth for all the fencing & window & air vents. Stay away from chicken wire! Have some type of netting over the run to protect them from hawks.
10 hens need at least 3 nest boxes, 20 hens 5 - 6 nest boxes. Ventilation is key to healthy chickens, make sure there is enough upper vent holes to keep the coop from trapping moisture & ammonia from the poop in the coop.
Build the coop close enough to the house, so that it is easy to get to daily & during bad weather.
Do you want a coop that you can walk into or just collect the eggs from the outside. Are you thinking about a pop door (electricity) or will you go out each morning to let them out. If you just want hens, have their window facing East for the early morning light, to give them more daylight during the winter. See which way your storms blow in, ours come in from the West, our door faces North. Is there a big tree not far from the house, during the summer, a tree would be a great source of shade during hot summers.
If you start out with 10 or so chickens, then decide you want more, make sure you have a separate quarantine area for any new chickens you get, and keep the new ones separate from the others for 30 days. Adding new chickens to an established flock is not pleasant, and it will take time for the new ones to find their place in the pecking order. You will have to keep a close eye on them to make sure they do not get injured or bullied.
I researched for almost a year before we moved, and had my list of chickens I wanted. Was able to complete the run while the chicks were still in the brooder. I also waited till late spring before we got our chickens.