There are lots of existing threads that might be of interest covering, as they do, the mortgage, insrurance, [PRTB] registration, tax, investment and other implications of renting out a former PPR.
It's probably a condition of your mortgage agreement that you tell the lender. They may charge you higher rates as a result, but you are free to shop around.
As far as I know, who resides in the apartment is irrelvant for block purposes, but the situation may be different for home (contents) insurance purposes.
All the questions can probably be answered by reading the various documents (mortgage agreement, leashold/management agreement, insurance policy). You may also want to read the Key Posts on property investment.
As far as tax goes, you will no longer be eligible for TRS and stamp duty clawaback may apply.