How many stages are needed depends on wether or not you use well water. You on well water?
Do you know the water pressure (psi) in the house?
BRS 150 gpd unit uses 2 membranes. Which can produce more product water with less water waste. But before membrane stages/cartridges get used faster, and it makes maintenance more tricky and finicky.
If your house water pressure is 50 or less go with 75 gpd or less. Or get a booster pump
Oh. I see you have posted your water.
5 or 6 stage. Chlorides and flourides need a carbon block stage or two to protect the membrane. I have swimming pool amounts in my local water and use two carbon blocks. Most of my particulates are of the same size, so one sediment filter before the carbon block is enough for me.
Getting a 6 stage is probably a safer bet. You could always run one stage empty if you don’t need it