Maybe you can use lorann oil to flavor your buttercream to taste like cream cheese instead of using cream cheese at all. ...only thing is I've read that it really strong flavoring so you only use a little bit to flavor the whole batch here's a thread about it.
I would put the cake together at the venue site because it gets heavy
There are tons of videos on how to tier a cake just Google how to tier a cake utube
I might be wrong but I believe once a buttercream has crusted there isn't much that you can do to smooth it out except treat that as a crumb coat and make more buttercream and ice over the cake than let it sit on the counter until lightly crusted than use a viva paper towel to smooth it out.