Hardware needs for multiple OpenVPN site 2 site servers

[bane]

Hi !
I am currently using a bunch (13) of OPNSense installed on virtual machines on multiple ESX.

I wonder, is there a limit of VPN tunnels that you can have on a single OPNSense (OpenVPN or IPsec aswell) ?
And is there an easy way to calculate what you need in term of hardware depending on the amount of tunnels and simultaneous hosts working on them ?

I actualy need to connect one OPNSense to everyone of my 13 others but I won't have more than 5-10 hosts behind this one.