My biggest problem with a large overstock like that isn't the here and now but the future.
In my opinion 50% water change weekly should be done anyway (not necessary)
So you may be keeping on top of the large overstock with large water changes but what if you decide to skip a week? Well nitrates get high. What if you go away on holiday???
I think overstocking offers no safty net
If the tank cycles to adjust to that many fish, which is totally possible, the big danger there, the lack of a safety net is because of the nitrates.
Fish CAN survive with high prolonged exposure to nitrates. It WILL kill them eventually, and it DEFINITELY can lead to disease.
BUT it is also easier to control.
You may need to do 50% water changes daily, (not fun) you can use plants, Purigen, or an algae scrubber to SLOW DOWN the rise of Nitrates,
Just remember Nitrates under 40ppm are considered (safe)
I have no problem keeping mine under 20ppm. (Usually under 10)
You will get to know your tank, you will figure our how much nitrates go up per day, you will see the correlation between nitrates and how much you feed. (The less you feed the better)
Being aware of how your levels are on a day to day basis FOR MONTHS will help you be prepared to deal with vacations, missing a week, unexpected time away, etc.
Over time you might decide it's too much work, and dump half your stock, or get a bigger tank.
This is pretty common for new aquarists. We jump right in, over zealous, excited, we have a plan of our gorgeous perfect setups, and are shortly humbled by the time and effort to maintain it, but it is very doable.
Be patient, keep at it, and you will find that balance between what is best for you, best for you fish, and best for your wallet.
That's really what it is all about, balancing those three things.