Can't say I know for sure if Mattamy will allow you to close without a kitchen through them. Even for people who deleted the cabinets above the range had a temporary 'floating' standard range hood in place. This is because they cannot close without the functioning kitchen.
As for the soft close cabinets, I believe you can order it through Mattamy, however a quick tip: you can get the soft close cabinet door dampers from IKEA
Unfortunately no one found out a quick bolt-on solution for soft close drawers yet