Do you have the chip in-hand? I'd be suspicious of a chip being sold as brand new from 2014. A lot of times, people simply lie or even worse, it's a scam. There are actually fake CPUs out there.
If cost is an issue, just get an air cooler for now. With this AIO, the amount of overclocking I would do on it is none. There's really no budget level at which a 120mm AIO makes sense unless, again, we're talking about a SFF or HTPC build.
its coming in later today from Houston, Tx, and I live in Austin. The seller was based there, had a 15 year ebay account with 100% positive reviews, and the seller offers a 30 day return for refund, something quite rare on ebay these days, and when I went to their website they seem to be a legit custom pc vendor for enterprise/workstation people, so an unused leftover CPU seems likely as companies with high budgets usually just buy whatever's newest. So If I get scammed on this one Id say they're just really, really good at it lol.
As for the AIO I currently have, it isnt failing or leaking, but the 1st 6 months I had it I had it installed with the RAD below the pump (was unaware at the time that was bad), and ive been pushing my 3770k on it so I figured why not start fresh. and yeah Ive seen the benchmarks about how the high level air coolers are on par with low-mid aio's for 2x the savings, I figured a aio loop would offer at least a more stable curve as the pump can be set with PWM and water is in constant flow in the loop, whereas with air coolers the air is turbulent, the pressure inside and outside the case can change, changing the flow of air through the fans, etc... So wouldn't the water cooling offer a more consistent peak temp while an air cooler could fluctuate in temp more at peak load based on current flows?