I used to have a little btc which sold and use in 2017-2018
I don't know what you bought that bitcoin for, but those years might have been a good time to sell. Hopefully you didn't lose too much money.
Be careful about going all-in on crypto in general, whether it's bitcoin, altcoins, or a mix of both--unless you're very young. If you're investing for the future, I'd be looking at the stock market as well. You can shield a lot of stock market profits from taxes as well, depending on what country you're in. There are a lot of tax-deferred options out there, and stocks can give you one thing bitcoin can't: income.
If you're going to be putting a good chunk of money into crypto, I would stick with bitcoin for the majority of it. If you've
got to buy altcoins, pick some of the biggies like LTC, ETH, and the like and don't stray from that. Once you start buying shitcoins you're just gambling. Nothing particularly wrong with that, but you don't want to be gambling with your life's savings.