Shop setting to disable checkout for specific account types

As a business user of a closed shop I would like to give option to register "read only" accounts, for customer who cannot place orders.

TECH:
Add shop custom attribute on SHOP_SF_CANNOTCHECKOUT_TYPES
Add API for checking is customer can place orders and also throw OrderException when placing orders for such customers.
Add customer specific attribute CUSTOMER_BLOCK_CHKOUT to prevent specific customer checkouts
Add customer specific attribute CUSTOMER_BLOCK_CHKOUT_X to prevent specific customer checkouts over X amount (YCE only)