Compete rainwater use for off the grid

Hi fellow permies!
I've been drawing up some rough plans on how I will use rainwater for showers and bathroom + kitchen sink. Basically, the barrels are aligned horizontally on the gutter line on both the front and back of the house.
#1 barrel is for filtration
#2/3 barrels are for cold water
#4 barrel is for hot water (ran through a compost bin that is cycled every month or so)
The three functioning barrels will be ran into new plumbing. Does anyone have any advice on this kind of project?

Thanks a lot!

The tanks seem small for primary plumbing system.
Does it rain often where you are?

Thanks for the reply!
Yes, I live on Vancouver Island so blessed with lots of rain. There would be two of these systems on the house (and a composting toilet-so no water needs for that)

It looks like you wouldn't need to have a very large water tank if you really have 1,152 inches of precipitation a year in Vancouver Island like Wikipedia says.
A word of warning from experience, it's better to use black plastic rather than the white because of algae growth.

It maybe better to use plastic pipe, although I don't know for sure. I remember that old turn of the century houses with rock water cisterns next to the house
would occasionally be struck by lightening and burn down.

Here is the math calculations to figure out how much water will come off your roof. I figured that a 1000 square foot roof with nearly 50 inches of rain a year
totals 40,000 gallons which means that you'd need to have a way to divert the excess water away from your house to prevent damaging it.

Awesome! Thanks for your research and tips... Will put in an overflow diverted into a cistern and look further into PVC piping!