I don't think GPU mining is guna "die" any time soon, eth or not there will always be something to mine with them, not to mention they are versatile and you can run all sorts of other algorithms (AI, chemical modelling, etc) as well if you ever need to pivot.

I'm curious why you want to go with s9's? they are quite old at this point, might get better ROI with something newer.

It looks like you are trying to go with index power rate? you gotta be real careful with that, if prices spike and you don't manage the miners in time (can happen overnight), your energy bill will basically ruin a years worth of profitability

Does your location already have power available? If you need to have oncor install more power, they are guna charge you potentially a lot ($40k+) and they *might* refund you a minimum of 4 years later.