Tips for first time moms & diapers? Deals, coupons, etc.?

Annie β€’ 23 years old. Diagnosed with PCOS & hypothyroidism. Married for 5 years. Ellie Rose πŸ’•πŸ‘ΆπŸΌ & Millie Jean πŸ’•πŸ€°πŸΌ
I have no idea where to start!
Are there websites with coupons? Anything I should sign up for? How do you get great deals on things like diapers and even furniture?