Unable to answer "What diameter is specified on the sign for this fire hydrant?" for osm.org/node/8582590735 via StreetComplete 56.0:

Can't see a sign nearby, is that the same information?

Attached photo(s):
https://westnordost.de/p/192423.jpg

Possible to go to the farm track here by foot and/or bike at least? Currently marked as noexit (meaning no one can pass this point), but it seems improbable that passing by any means of transport is not possible.
How does the situation look on the ground, which vehicles and people can pass north/south here?

Unable to answer "Do these steps have a handrail?" for osm.org/way/55832336 via StreetComplete 45.2:

No steps here, steps are further south on the way there. Roughly a few meters away.

Is this building/position really part of Habsburgerallee 57-59? Where is Helmholtzstraße 28 then?

The name "Im Rebstock" is listed as existing as a street name in Frankfurt am Main and it might be here because it was mapped this way in the past and is listed elsewhere.

Does this street have an (official/unofficial) name?

is this a new building? visible on orthophotos and satellite images. i couldnt judge what belongs to the building exactly, maybe someone with local knowledge can help?
Also: is there a connection to the building north of it through which one can walk?

public Transport ticket vending machine not here