As much as i hate eth, i would advice you to mine eth in these days.
Whether you hold your eth or convert them into bitcoin is up to you, (i would go %10 eth, %90btc) but as a miner's perspective; eth is no brainer to mine. Eth or anything else which has GPU support.
Bitcoin home mining is long dead. You'll need to buy hardware from Bitmain and if you have any problems with your miner, you'll be having one of the worst customer support experience there is. I don't know which part of the globe you live on but you'll probably wanna take notice, Bitmain is located in China. Buying them is a pain, selling them is a pain, operating them is a pain, if you have any problems you'll be experiencing the real pain. Bitcoin mining is a no no.
On the other hand, you can grab a few AMD or NVidia gpu's from the local PC store of yours (maybe even used ones) and you can start mining eth right away. No need to tell, you'll get your ass covered immediately by the companies if you have any problems. I can write a page about the benefits of home mining but you probably already got the idea.
TLDR; Just mine eth and save yourself from endless pain.
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How much you need to invest? Depends on your budget. A GPU is around 200$. Many people run 6 of them. The other parts are dirt cheap. 1700-2000$ would build you a nice GPU rig.
A single antminer s9 is 2700$
https://www.amazon.com/Antminer-S9-16nm-Bitcoin-Miner/dp/B01GFEOV0OAwesome, and I'm thinking like you when it comes to ETH and BTC. But yes, that's not relevant when thinking about mining... Give the people what the people want...
That investor could throw in 100,000 - 300,000 €. He would rent a hall, this is certainly not about mining at home. I'm just thinking about how to use all of this money most effectively. So just multiply all of the numbers? Or is there is more effective and expensive gear available?
And thanks for that Antminer link, I have to learn the basics of the basics.