well, i already had a VPS i use for DNS, email, web hosting, ftp, etc, so I was looking around on how to set up your own seedbox.

this guide (no affiliation) was quick and easy to follow: Seedbox DIY Guide - Seedbox Server Configuration - Seedbox Hosting

Using gentoo and not CentOS (just emerge transmission)

Ignored the firewall part (gentoo doesn't filter any ports by default)

Follow the rest of the guide.