Hello and welcome to BYC
You've come to the right place! O.K. Questions...
1. It's up to you, how much time you have, how much effort you want to put into getting started... Chicks are more fun, but you will need to keep them warm until they are strong enough to live outside etc and wait longer for eggs, but they will be used to you and tame... POL pullets on the other hand will be easier, but could work out more expensive and they will possibly not be very tame. If you don't want roosters you can buy sexed chicks and if you buy older chickens you can choose only hens. "Straight run" chicks are unsexed.
For places to buy chicks/chickens I'd suggest you look here:
https://www.backyardchickens.com/f/16/chicken-breeders-hatcheries
https://www.backyardchickens.com/f/67/buy-sell-trade
2. How much space have you got? What do you want them for? Eggs, meat, as pets with the benefit of eggs? All I can say is you should get at least 2, as chickens are social creatures who do better with a companion.
3. Depends again on what you want them for. Meat and eggs, only eggs, pets and eggs? Have a look here:
https://www.backyardchickens.com/products/category/chicken-breeds
http://www.ithaca.edu/staff/jhenderson/chooks/chooks.html
4. If you are building from scratch there are a lot of options. You can buy in materials, use recycled materials... The only things limiting you is your budget and your imagination! Here's some sections to look at for ideas:
https://www.backyardchickens.com/atype/2/Coops
https://www.backyardchickens.com/f/9/coop-run-design-construction-maintenance
Since you are a newbie to the chicken world I think I'll throw in one more thing for you to look at:
https://www.backyardchickens.com/atype/1/Learning_Center
Enjoy!
