Proxy Question

Hello BHW, i need some advice about proxy setup.
I want to order my ISP my own static IPs to configure my own residential proxies to use them for instagram mainly.I will use the Ips only for instagram ,so my question is what i need to configure my own residential proxies with my own IPs and how many acccounts i can hook up per IP.

Also one question off topic ,how is possible thousands of people using mcdonalds wi fi daily to use their instagram accounts,how they not get flagged etc ?

Thanks any advice will be helpful