iVentoy and Ventoy are two completely different software, but both come from the same author.
Please install the VC++ runtime library for VS2019 firstly. Microsoft Official Download Link
YES. Please refer About Secure Boot
NO. But iVentoy can work together with third-part DHCP server, please refer: About third-part DHCP server
The client and iVentoy can be in the same LAN/VLAN or in different LANs/VLANs. Please refer: About third-part DHCP server