For higher ROI don't take the bet on BTC only, yes it's the safest option bit for better gains you need altcoins as well, even Ethereum would do just fine, now that Pos and the better gas fee are around the corner Ethereum will perform very well from now on.
The same altcoins that may get you rekt? Altcoins may be promising but I don't think they are safe when the market is crashing, they can give you huge ROI but can also take all that you have invested.
If you can afford 1$ a day it is not a bad idea, but personally, I will wait every weekend and sum them up together and then buy bitcoin weekly, I don't think there is any platform right now where you can buy Bitcoin as low as 1$ right now, you may even struggle to send it to your own personal wallet due to fees and doing daily buy may accumulate plenty of taxes on every transaction you do, you will have to buy from fiat every single time with each of it taxed.