New heating due to shutdown

Hello everyone,
I have fulfilled my wish and bought a house with 254 sqm of living space. The house has an oil heating system from 1985, which was decommissioned in 2015. Now I want to renew the whole system. I have dealt with the heating system and would like to buy the following.
Buderus boiler Logamax GB125-22 kw
Solar with 6.27 sqm
Water storage SMB 300
The whole thing is a package.

Now to my questions: Am I allowed to install it that easily? From when does the chimney sweep have to be called in? I assume that he has to approve the whole thing.
How does such a process work? What else should be considered?

Regards

Are you only doing the heating for the house? Is the house already insulated? Do you want to install the heating and solar yourself? Basically, the heating is installed and afterwards you call the [Schorni]. He comes by, measures, checks, possibly criticizes, and that's it.

The house is being renovated. The roof is already insulated. The facade is still pending but will be done in the future. Yes, I want to do everything myself or without a company.

Is there a guideline or something similar to pay attention to? Or do such inspections usually go smoothly? What would be the tasks of the chimney sweep during the inspection.

Best regards

Checks whether the system is basically safe and complies with the legal limits. Do you have experience in the [handwerklichen Bereich]? I assume that the heating system you selected will be too large in terms of heating capacity. Especially after further insulation measures.

I am well skilled in craftsmanship. However, I haven't done much heating work so far. But I fully trust myself to handle the conversion.

Do you think it would be too strong, so should I take a weaker one?

I personally cannot assess that, but based on your rudimentary description, I assume so. I am only an interested layperson myself, but I have read up on a lot. You should do that too. You have made a start.