If you are planning on saving a significant amount in bitcoin I would suggest a cold storage wallet like trezor or cold card. Buy the wallet direct from the manufacturer, don't try to get a cheaper option, that might be compromised.
Once you have that set up continue DCA or your current stacking method on your preferred exchange (ideally one without super high fees) theres a super good intro to this on r/bitcoin on reddit.
Lightning and any other layer 2 should be for small transaction and amounts.
Certainly not the only way to do it, but its the safest. I had bitcoin in celsius when it collapsed and lost a good bit until earlier this year when I was able to get some back through PayPal.