If your main power line is max. 100A, you should try to avoid going over about 80A of continuous usage, ballpark figures.

Let's see: 80A times 240V that's somewhere around 19.2kW and about 460kWh per day if you use it all day long. That is some serious power budget and you have to keep it safe. At the currents that beefy mining rigs drain, every connection is a potential fire hazard. You will see how hot cables and power connectors can get.

I don't ask how such an amount of energy could be for free. Frankly, someone has to pay for that and it's a lot. You say, it's free for you, you do yours, none of my business.

If you run this amount of energy through mining rigs, you should not forget, that basically all of this energy turns to heat, whatever cooling you use, you must get rid of roughly 460kWh heat if you go to the limits. Immersion cooling might be more compact, but you still have to get rid of 460kWh of heat out of it. And the cooling will eat some part of your energy budget.

Don't try to start big at once as you're no way experienced in the mining business.

Here's a mining profit calculator that can take difficulty rise into account (which many calculators foolishly don't, for whatever reasons): https://jblevins.org/btcmpc/

History shows that mining difficulty rises in the long run, your hash power usually not, unless you add gear, but that means, more investment, longer periods for ROI. And Bitcoin is volatile, too. Atm, all is nice and shiny. It won't stay that way all the time. Oh wait, you have a limited "free" energy budget, you can't add gear past it. So, diminishing returns are inevitable for you. Take that into account!