I'm finding very little about the initial infection vector. How does it infect a machine?

Also port 53/udp is an interesting choice for communicating. Many enterprises redirect that to their internal dns.

Start a no server demo here and you can try Actual out yourself:
https://demo.actualbudget.org/

That way you can try out the Starting fresh steps for real or go through their Tour interactively instead of just reading:
https://actualbudget.org/docs/getting-started/starting-fresh/
https://actualbudget.org/docs/tour/

I never recommended the Intel N chips though. :)

A cheap N100 or N305 mitx with more ethernet and sata ports already attached is one thing, but I wouldn't wanna risk warranty hell with more money on the line.
Considering you are gonna add a dgpu I would look at a low tdp desktop cpu such as ryzen 7600/9600 from a trusted store instead.
https://forums.servethehome.com/index.php?threads/topton-warranty-practices.40421/

Reviews on Steam makes it seem promising, but I'll wait for a gog.com release before buying.

00:00 Virtual Files Systems Improved
02:03 CRC CPU Arch Updates
05:44 Less Network Latencies
08:03 Handling Data Loss on File Systems
10:01 Fix for 1993 ELF Binaries
11:24 Apple Silicon Updates in Kernel
13:02 Zeroing out SSD Improvements
14:34 Mobile File Systems
15:50 WIFI 7 and Networking Stack
17:12 BCacheFS Kernel Updates & Drama