CBSubs can not add features that do not already exist in an extension. If com-properties does not already keep track of the number of houses a user has and does not allow setting a flag to to only permit a number of houses to be posted then CBSubs can do nothing for you as it can not add features to an extension. If it does and is handled by way of database you can use CBSubs SQL Actions integration to update the users database row with a new value based off plan selection.