From what I'm looking at, the Infinity DB schema doesn't look different from vichan's at all.
If this is the case, it should
be a straightforward transition. However keep in mind hotwheels/ctrlcctrlv didn't intend for users of Infinity to migrate to Tinyboard/vichan, as they are different software in terms of behavior.
To make sure you have a smooth ride, I'd backup the production site and try running a transition on a local machine first
if I were you, just so your chances of having a bad day are reduced. If you notice any errors trying it, feel free to put them in this thread.
As for PHP support, I can guarantee compatibility with 7.3, and will support 7.4 as soon as it released on distros.