can I use a 2017 iMac running Ventura as my main display for a Mac mini

No. Target Display mode is not supported on Ventura or a 2017 iMac.

Get an actual display for the Mac Mini, or use Screen Sharing from the iMac to see the Mac mini's screen, though it will be windowed, and probably very laggy.

You will also need an actual monitor connected to the Mac Mini to set up Screen sharing on it though.

click here ➜ Share the screen of another Mac - Apple Support

You might look into Duet Display or Luna Display

both would likely need you to have a "real" monitor as main monitor at least for setup

if you decide to go with a normal monitor then the good news is a monitor would use a lot less power then using a full computer like an imac in target display mode would be.