Fortinet Fortigate 40F configuration

Yes, it supports load balancing between servers using virtual server configuration (ref: https://docs.fortinet.com/document/fortigate/7.4.1/administration-guide/713497/virtual-server-load-balance ).

You can also install SSL certificate with intermediate CA. Is this for deep inspection? 

Hello,

1) load balancer between the 3 servers

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Setting-up-a-VIP-load-balance-with-HTTP-host-check/ta-p/198274

"- It is important to note that there is a limitation for the number of real servers which can be configured under every VIP, check for the platform and FortiOS version used, by using the command 'print tablesize'  or check the Maximum Values Table portal. Look for the parameter 'firewall.vip:realservers' which will show how many real servers can be configured for every VIP object. For example for 100E and FortiOS 7.2.4, the value for 'firewall.vip:realservers' is 16 which means 16 real servers for every VIP can be configured."

In order to find 'firewall.vip:realservers' please navigate to https://docs.fortinet.com/max-value-table, specify hardware model and firmware and search for 'firewall.vip:realservers'.

2) installation of an SSL certificate with intermediate CA

It is not clear which certificate is supposed to be imported. However please find link below which you may find useful:

https://docs.fortinet.com/document/fortigate/7.4.1/administration-guide/907098/import-a-certificate