You can NEVER offer to pay an employee "after the first milestone" If anything you will be LOSING money running a server. First of all there in NO guarantee the server will succeed, if you want to make money then you will be needing to offer inn app purchases and i doubt that a new player to the server will want to pay off the bat to get a new rank, or get crates.
Telling people that they will "be paid later" is also a form of FRAUD, witch is a crime btw. and not only to mention WHO WOULD WANT TO APPLY. To create plugins is NOT easy, it takes years of studying to get to the right level of coding knowledge it takes to just create a plugin when you need one.
*BUT Mojang pays people to run servers right, i saw it on the website* you may be asking. Well yes, they do pay servers to run but for one reason only, the servers are a partner to Mojang, Mojang makes money with the popular servers like Mineplex
My advice is to scrape together enough money to keep a server open for a few years, if you want employees then also get enough money to pay them the first week and so on, (i suggest $7.00 an hour until the week ends for Each person.
You can TOTALLY make money from running a minecraft server but you can NEVER make people work for free until you get to the milestone, that is illegal.
Do your research on economics and start a minecraft server with your friend or someone who has at least a basic understanding of commands. There are multiple tutorials that teach you this stuff on how to run a server and how to make money.
good luck and when you get it started ill be happy to check it out when it is open, just remember dont offer things you dont have any guarantee will work.