Just curious, why do you want to change all piping if there is no leaking and fully usable?
The same goes for the pump.... and for pump, it is even easier to replace.. so might as well continue to use it.
As for the water tank, if you are in Selangor area, keep it, it is never overkill, you don't know when the next water disruption. Just clean and wash the tank up will do. By the way, you might also want to know how the water tank and pipe is being routed. Does the pump get water from all the tank or some is left idle?

The lifespan of pipe and tanks are way longer as mentioned by other forumers as well, no worries

It is very easy to determine is there is leak in your water pipe for those that have pump
First you need to ensure all your piping route, if they all get the water from pump, then easy peasy. Just on your pump and check the water pressure gauge if it drops rapidly or the pump keeps running even all the tap is close. If the water pressure can hold and the pump is not running when all tap is close... then there is no leak. Thus no changes required

Yes... spend some money to get a plumber to check and draw out the full piping route for you. The pump, the non-return valve... the hot water piping... the pipe size and material, even to the kitchen and garden pipe which usually contacts directly to the main.

For usable, turn on the tap, check the water pressure, check the mixer, hot and cold water funtioning...
For overflow, just press the floating ball valve and see that if the tank is full, can the water overflow successfully.... as you have 7 tanks, you need to know how the tank is routed, are then link or operate individually and check them one by one... again, get the plumber to do the test from you while he is checking the full house routing.
Besides, that, also check the emergency release valve is operation by letting water flow out from the bottom of the tank....

Basically that's it. Once you have the full route of your piping, then you can share and more information or guidance can be provided.