Hi Niek and welcome to the forum. It is always a good to crosscheck the buildings mapped in your place from time to time, add new ones and complete the tagging if necessary. By doing so it is a good idea not only to complete the addresses but also check how the building itself is tagged (residential … house … detached … garage etc.) and make corrections if necessary. Many buildings are just mapped as building=yes so this could be improved. Have a look at the wiki page mentioned by @ToniE for more details.
In regard of the address tagging both options are regularly used - tagging the address directly to the building or adding a separate node to the building, usually where the entrance is. See the wiki page key:addr. for more details.
The general recommendation is to follow the tagging scheme which is already in use for the majority of the buildings in your area. Here in my area most addresses are tagged directly to the building itself, so if I get in touch with an address tagged to a separate node I usually move it to the building, but I would not do that if I work in an area where the majority of addresses is tagged to nodes like in your screenshot.
In some cases (multiple entrances with separate addresses for a single building) the use of address-nodes is the best solution.