I'd be cautious about investing too much in this.
Certainly in the first case it'll only be houses with 4 or more bedrooms which is a minority of houses. Then a number of people will avoid them by selling as 3 bedrooms and a study etc.
The house of Lords has already called for the legislation to be revoked and the National Association of Estate Agents is opposed to it too.
With the prospect of an election in the not too distant future I can see the distinct possibility of all this being withdrawn in a year or two in which case you'll have wastedyour time aand money