Yes, the Feed-In Tariffs only apply for systems up to 5 megawatts. That’s pretty big so will suit all household uses and most businesses, except for large factories.
Systems between 50kW and 5MW can alternatively choose to use the Renewables Obligations.
The Government has not yet finally decided how it will define ‘capacity’ – the parameter used to define where the tariff levels are set. Logically the so-called ‘declared net capacity’ (DNC) should be used to allow for variations between renewable energy types.
Not unless you are in receipt of tariffs for more than 25 solar PV installations. If that is the case, you will receive a lower tariff. These lower tariffs are in the third column of the table linked here, and described in the footnotes to this table.
Many but not all – the list is shown here.