My webserver (which runs a lot more than just the osTicket production site on it: MySQL and a couple web based DB apps.) currently has 6 cores, 32GB RAM, and 200gb HDD. This is over kill as it ran just fine back when it was 4 cores 16 gb ram for around 400 users, 5 agents. When it also ran two additional osTicket production sites, our intranet, our 5 external websites (WordPress).