Yes there is chance of disease but quarantine works well with new birds and should always be practiced. The chicken math will take over once you have your birds, I know my flock grew inexplicably :gig Good luck with your 8 new feathered friends :thumbsup
Hi :welcome
Glad you could join the flock! The learning centre has some great articles on housing your chickens. Here is the link https://www.backyardchickens.com/atype/1/Learning_Center
I would suggest you build bigger than you anticipate as flocks can grow alarmingly fast. I would start with...