Hi, buying bitcoin should not be in your list if you are not prepared for a rollercoaster ride. Try to understand the market first. Bitcoin's blockchain technology is created for decentralised spending but then the feds took hold of it because of it's illegal use in the black market, they created ways to trace the back then untraceable transactions. Right now the value of bitcoin is purely speculative because of the involvement of large institutions, also you need to consider it's market cap, where when all the bitcoin had been mined the value will probably skyrocket or stays the same. You need to understand what's driving the market, why Bitcoin has such value. Try researching on other cryptocurrencies too, what is their use in the future etc. I'm sure that there will be something like bitcoin waiting to happen on altcoins.
Also, a platform like coinbase, binance, robinhood etc. Is not good for storing your cryptocurrency, as you said it, it is a platform and is only good for trading. A money in the bank is not your money until you widthraw it. Same goes for these platforms, get a cryptowallet in this way you hold your own cryptocurrency.