make the letter “m” in front of lat=… and lon=… so you get a marker on the osm-site on your building and you can put this link on a website.
yes and no… OLM is a part from openstreetmap.de. But if you edit something in openstreetmap.org, you will see it automaticly also in OLM… OLM is just a layer, which will display some additional infos, that you can’t see on the official osm-website (there are a lot of other layers… p.e. opengastromap, Maxspeed,…
30089216, in this case, is the building outline’s id.
That’s what, for example, the people at flickr are using for their OSM links. However, this method is somewhat fragile, as the object id might change due to certain edits (such as splitting a way, deleting and recreating an object, or replacing a node with an area). Unfortunately, there’s no better method at the moment.