This business you have tagged as 15 Clarence St but have mapped at 50 Clarence St. The company website lists it at 50 Clarence St.
https://heroshotphotography.com/contact/
Which is correct?

I am shifting the business tags from the building to a separate node at this site...401 Collins Street, but noticed your web page has the Melbourne Main Office at 220 Collins St.

https://heroshotphotography.com/contact/

Which is correct please?

remapped using building part method

...and mapped as simple polygons

The simple buildinds that were changed to multipolygons and were likely created by iD due to your mapping method are deleted.

Hi _mark
are you able to put the correct apartment names on both these buildings

Would shop=photo be suitable for the business
shop=photo
Although the craft tag is correct, I don’t think the craft tags get rendered on most layers so an additional shop tag may display better.

Hi, the multipolygons here are invalid.
https://tools.geofabrik.de/osmi/?view=areas&lon=144.98697&lat=-37.92507&zoom=17
osm.wiki/Relation:multipolygon

The tag addr:floor or addr:unit may be applicable

You have added the business address to the whole building.
If the business occupies a floor or unit within the building, you should add a node within the building outline and add the business tags to it instead of the building outline.
Same goes for interstate offices.

Hi, does this company occupy all floors of the building?

Hi, there is nothing to indicate a wilderness hut on imagery in this park. Was it added in mistake?

I should add that osmi areas picked up the invalid multipolygon
https://tools.geofabrik.de/osmi/?view=areas&lon=152.95314&lat=-27.25959&zoom=19

If you really want to use a multipolygon for this you could have the two building parts in the multipolygon as role outer and remove the central part from the multipolygon and tag it as a roof.
You would then have a valid mp as the 2 buildings do not touch and the roof would render when tagged separately.

Hi, the museum is mapped as a multipolygon but it is done in a way that is invalid for a multipolygon in osm. Outer parts cannot join each other. We have a wiki on multipolygons that explains this.

osm.wiki/Relation:multipolygon

I suggest that you delete the multipolygon and just map as two individual buildings and the the central part should be mapped as a roof instead of a building as it is just a covered walkway linking the two buildings.

Another way to map the museum is to tag each bit as a building part and then add another polygon (tracing over the outside nodes) around the entire outside of the three parts and tagging that as a building with the museum tags.
building:part=*
Building part method is mostly used for complex 3d buildings but is also useful for outlining parts of simpler buildings.
Unfortunately the individual buildings parts are not rendered in the layers available at osm.org, only the surrounding shape.

Another method is to just trace one line around the museum and tag that.

Hi, welcome to osm. Did you intend to have this mapped as a multipolygon?
relation/18058167#map=19/-37.713027/145.113445

I have tried to fix all the remaining errors by @Bharat13 in
changeset/156674843
changeset/156674966
changeset/156677475

In Josm, I would create the relation first and then open that relation for editing. In the relation edit window you can add all the ways in the expected order and add the roles for the ways.
I am not familiar with using the iD editor.

If you find an interest in creating these types of relations, I expect you would find it more easily done using the Josm editor.

Sorry I can be of help as I am unfamiliar with tagging route relations.
You can get plenty of help by asking on our community page
https://community.openstreetmap.org/c/communities/oceania/73

Seem to me that you may need to read about route relations
osm.wiki/Relation:route