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
NO. In UEFI mode you must disable secure boot in the BIOS before use iVentoy.
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