Hey Lisa. I can lay something out for you in CAD, but I dare say what you're trying to accomplish is nearly impossible. Your parcel is a triangle shape, which doesn't do you any favors for a parking lot layout. Sharpe corners are inefficient. I do not think your "shared parking" idea will fly because that MF development to your west likely built to the minimum parking standard already. I like @Account Closed's suggestion of having parking underneath the perimeter of the building.
Stormwater detention can go under the surface parking lot at a cost of about 2-3x traditional BMPs, but that could possibly offset the additional cost of deck parking. Your tract naturally slopes southwest toward the point of that triangle, which would be difficult to build inside anyway.
I think there's a required 20' perimeter buffer when commercial is adjacent to residential of any kind (SF, MF, etc.) but I need to refer to the UDO. Good news is, that buffer can count toward your tree save in most municipalities. Tree saves are typically negotiable thru mitigation money anyway. If you're already zoned O-1, then develop by-right and don't offer the adjacent houses any land.
May I ask; why 2 levels and why 18k SF? Have to discussed this with a Buyer?