Grown as a 'bush' is perhaps a bit of a stretch - this is really a shrubby small tree, either single or multi-stemmed. Which form you choose is up to you and what you find available.

However, I would probably select some other plant for this purpose anyway - Amur maples have very pronounced invasive issues in many areas and they are not highly recommended.

OK, tree it is. The local
recommendation is to plant it more than 100 yard away from natural areas, hence
my place is a non-issue, I hope.

I am reading opinions
like limiting the tree to 3 stems, I wonder if that's only aesthetics (odd number of stems) or a real
crowding issue.