I need help setting up my Synology Nas to work with my Asus Router

Setup to external access to the NAS and then help with the firewall, DDNS connection to Open VPN server and do any port forwarding needed with correct connections. Make sure I am getting the connection out safe and able to share links and create users on Synology Drive with clients to share like I do with Google Drive. Have the best and practice for a video production company. Located in Chicago able to literally physically help me with this. I am so frustrated and have set quiet a bit of this up I am just really confused on a few things. using ASUS RT-AX86S and a synology ds1621xs+ 6 Bay 16T NAS. I also have a qnap network switch and use a Mac Studio for the main connection points.