Since the price of the new miners are ridiculous high I was thinking to buy 70-100 S9 Antminers  that I have sourced.
I have the following questions regarding the Antminers S9's:

1) What is considered a good price for the S9?
2) What is the most stable version? Is the 13.5 THz the 14THz S9J?
3) What is the life expectancy that see those miners will have, since the coming months there are tons of S19 and other modern technology miners arriving in the market and the current difficulty skyrocketing?
4) I have calculated the break even point at around 110 days in a price around $300 and the price of 0.06 cents. Does it make sense to purchase with that ROI?
5) Is there a trustworthy overclocking firmware? I have read all the relevant topics from the forum but I didn't found anything that seems trustworthy. Does is makes sense to immerse cool them?

Any other advice is highly appreciated and thank you in advance.