Rescued a half-built V2.4, where do I even start with the wiring?

On the harness, I'd redo anything that looks half-arsed rather than testing as you go. Bad crimps have a nasty habit of passing a continuity check on the bench and then giving you intermittent dropouts six months in, and hunting an intermittent fault on a moving gantry is misery. What I did on my 2.4 was pull the connectors off one at a time, recrimp anything dodgy, but leave the wire runs themselves in place if the loom is tidy. No point stripping the whole lot if the routing is allready done and sleeved, that's the tedious part. Check the crimp on the stepper and hotend connectors especally, those are the ones that get lazy. A proper ratcheting crimper with the right ferrules makes it a quick job, honestly half a Saturday. While you've got the panels out, that's the easiest time to do the wiring anyway, so the timing works in your favour.

For the acrylic, don't try to reuse the old foam tape that's already been stuck and peeled. Peel it all off, clean the extrusion with isopropyl, and lay fresh double-sided foam tape in a full loop around the panel edge, leaving the corner joints butted not overlapped. Then rest the bottom edge in first, lean the panel back against the frame, and push the top corners in one at a time with the flat of your hand rather than your fingertips. Cold acrylic snaps easy, so if the garage is chilly let the panel warm up indoors first. That's what cracked most of mine the first time, working on it in winter. On the printed parts, since you're reprinting the cracked brackets anyway, consider doing the hotend and toolhead area parts in ABS or ASA rather than whatever the original set was. Those see real heat and 2022-era PETG parts there tend to creep. The rest of the stock parts are fine as they are if they look healthy.

Get the frame squared with the belt tension trick from the manual before you worry about anything else, then it's all downhill.

Lucky find, mine sat half built for a year too and it was the best way to learn honestly, everything already mistakes-free at my own pace. One thing I'd add, since his kit is from 2022, check the printed parts against the current manual before you reprint anything. A few of them got revised since then and you don't want to duplicate an outdated bracket from the old files. Also dig through the bagged hardware and count the screws against the BOM now, mine was missing a handful of M3s and finding that out mid-build was annoying.

Bagged and labelled is a good start but don't trust it blindly. Mine came the same way and I still found three diffrent bags all missing the same M3 screws somewhere mid-build, which stalled me for a week. What saved my sanity was going through every bag against the BOM before touching anything, then sorting it all into a cheap fishing tackle box. Sounds overkill but grabbing the right screw mid-assembly without digging through baggies is worth the half hour it takes.

On the 2022 vintage, flash the firmware fresh before you even think about first boot. The board might be sealed but whatever was loaded back then will be a couple of major versions behind Klipper now and the config format has shifted since. I resurrected a friend's half-done machine last year and spent a night fighting an ancient config before I just wiped it and started clean off the current sample file.

Also give the belts a proper look. Two years coiled up in a box in a garage will put a memory kink in them if they were stored tight, and a kinked belt shows up as ghosting nobody can diagnose. They're cheap, just swap them if they look wavy.