I have been told recently that if you put white vinegar in a watering can, pour it on the weeds, they will die. Not as permanently as with round-up brand weed killer but enough for you to get in there and see what you need to do to make sure the fencing is secure and won't allow predators in. After you get the chickens in you should have no weed problems.
Since you and I are in the similar area of the US as regards to winters, I suggest you read up on a thread here https://www.backyardchickens.com/forum/viewtopic.php?id=421122
Also, read through the FAQ on this BYC forum as they are very informative for beginners and experts alike.
We can't tell you how many birds you can house with certainty because you have not told us the breed of birds you are interested in. I suggest a cold hardy breed, dual purpose bird. Ameraucana ( my breed), Easter Eggers (they are not a breed - more a type) or any of the peacombed, breeds would be best for you. They are easy in the winter and the roosters can be slaughtered for food. You should, for utilitarian issues stay away from the bantam breeds ( small birds) and look for breeds that have "LF" after their names. LF means Large Fowl". If you are looking to get true breeds or you have children who would like to show, you must get your birds from a breeder - not a hatchery, no matter what they say on the descriptions in their catalog. You can go to some hatchery sites to read up on the different breeds as to their cold hardiness, egg production, egg color, and apropriateness for butchering. The Hatcheries can sell you mixed flocks of various birds too which are " cold hardy" "colored egg producers" "meat birds", etc. You wuld then have a colorful mix of mutts ( mutt is not a derogatory word in the chicken world if you are not showing ) who will be as much fun to watch as they are for your family. Just depends which way you want to go.
I recomend you get all your birds from one source so they can grow up together and they will develop a pecking order as they mature. Introducing new birds is not as easy as you might think. Vaccinated birds are healthy birds. Most organic programs allow for vaccinating your birds. You should do it. What you don't want is for a bird to get sick, have to be treated with antibiotics and/or infect your entire flock. It take a long time for antibiotics to leave a bird's system and it will remain in the meat and eggs.
There are lots of opnions on BYC. This is just mine. We all share our opnions and we don't always agree, but we are all trying to be helpful. In the end, it is your decisions that will win because it will be your flock. Your family will care for and eat the products from your flock. Do your research and you will love raising chickens. They are affectionate, sweet, warn you of intruders, and provide food for your family.
Enjoy your new endeavour and
