Honestly, just grab the Arctic Liquid Freezer III 360mm AIO. It kills the temps, fits the 4000D fine, and saves you cash compared to the Noctua NH-D15 Air Cooler.

Jumping in here because I actually went through this exact same dilemma last year. I was terrified of a leak too, so I went with the Noctua NH-D15 chromax.black Dual Tower CPU Cooler for my build. Honestly, it is a monster! It keeps things super cool and you never have to worry about pumps failing or liquid spilling everywhere. It fits in the 4000D, but man, it is massive, so make sure you check your RAM height first. If you want something that performs just as well but feels a bit more modern, you should totally check out these:

• DeepCool AK620 High Performance Dual Tower CPU Cooler - it looks so sleek and keeps my temps surprisingly low during long renders.
• be quiet! Dark Rock Pro 5 120mm PWM Fan - just silent, like its name says, which is amazing if you have your mic open for work calls. My experience was that air cooling is just stress-free. Since you are on a tight deadline, you dont want to spend hours messing with radiator screws or cable management for an AIO. Just slap a big air cooler on there, make sure your case fans are set up for good intake, and you are golden! You got this!

Re: "Jumping in here because I actually went through..." - totally get the anxiety. I remember sweating bullets installing my first AIO, thinking the whole thing would dump coolant on my gpu. It worked out fine, but the maintenance aspect is definitely real. Are you planning to overclock that chip, or just run it at stock settings? Might change how much headroom you actually need.