But here are the downsides:

Such a system is more expensive. An indirect heating boiler for 150 liters costs 35 thousand, and you still need automation, an expansion tank, air vents, a circulation pump, and so on. It is also better to involve an experienced plumber in the work.
It is unlikely that you will be able to place the boiler and water heater directly in the house; you will need a separate room -a boiler room.

What are the features of a boiler operating on gas from a gas tank?
A gas holder is a special tank with a capacity of 3000-5000 liters for a gas mixture of propane and butane. It is usually buried in the ground.

The main problem with gas holders is working in winter.

When a gas boiler is working, propane evaporates first, as it is more volatile, and then butane: it needs a fairly high temperature to evaporate, about -0.5 C. I have encountered situations where a low-quality gas mixture was pumped into a gas holder and the butane did not evaporate in winter, and the boiler stopped working. Therefore, I recommend working with trusted gas suppliers and buying gas holders with a heating system so that gas is supplied to the boiler without interruptions in winter.

Another option is to use 50-liter gas cylinders, but they run out quickly.

How long one cylinder will last depends on the boiler's performance, but in my experience, I had to refill them every two or three days.