ᐅ New Heating System Due to Decommissioning

Hello everyone,
I fulfilled my wish and bought a house with 254 m² (2733 sq ft) of living space. The house has an oil heating system from 1985, which was decommissioned in 2015. Now I want to replace the entire system. I have looked into heating options and would like to buy the following:
Buderus Logamax GB125-22 kW boiler
Solar panel system with 6.27 m² (67.5 sq ft)
Water storage tank SMB 300
This comes as a complete package.

Now for my questions: Am I allowed to install this myself so easily? At what point does a chimney sweep (or flue inspector) need to be involved? I assume they must certify the installation.
How does this process usually work? What else should I keep in mind?

Best regards

Are you only working on the heating system in the house? Is the house already insulated?
Do you want to install both the heating and solar system yourself?
Basically, the heating is installed first, and afterwards you call the chimney sweep. They come by, measure, inspect, possibly point out issues, and that's it.

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

Is there a guideline or something similar to keep in mind? Or do these inspections usually go smoothly? What would be the tasks of the chimney sweep during the inspection?

Kind regards

It checks whether the system is basically safe and complies with legal limits.
Do you have experience in the trade or construction field?
I assume that the heating system you selected will be oversized, especially after additional insulation measures.

I have good craftsmanship skills. However, I haven’t done much work with heating systems so far. But I am confident that I can handle the renovation completely.

Do you think that one might be too powerful, or should I go with a weaker one?

I personally cannot assess that, but based on your basic description, I assume so. I am just an interested layperson myself, but I have read up a lot. You should do the same. You have already made a start.