Article 4 Portsmouth

HMO Licensing

Hi,
I am considering buying a property in Portsmouth in which the Article 4 direction will apply from November 1st onward.
Do I understand it correctly that one can still buy a property now and rent it out to 3-5 unrelated tenants (before November 1st) and then be able to keep the small HMO status going forward? Will I need to notify the council for the change of use (C3 to C4) and can they refuse it or is it part of my permitted development rights until November 1st and can't be refused? Will there also be restrictions regarding size of rooms, number of toilets, wash basins etc. before or after November 1st? What if one hasn't found a tenant by November 1st, does that mean that the right to a small HMO is gone forever unless one successfully applies for planning?

Many thanks,
Christian Schackmann