you will need to add soil which has a more sandy content.
May also be advisable to add soil improver which might help to break down some of the soil.

unfortunately not as the clay does not hold water and your topsoil will become waterlogged ,killing any plants and becoming a bog,if you want to make a garden out of it ,remove the clay to a depth of around 750mm line with a breathable membrane shingle around 250mm ,subsoil 300mm then topsoil 200mm ,costly but it will be a living garden.This problem occurs a lot on new build sites where the use the spoils to build up the gardens to save monet ,then sprinkle topsoil on top to make it look pretty,dont find out till you start to dig it that it is just crap.

Yes, that will work fine. You could even go a little further and add 1 inch of sharp sand first that will help cut the clay over time, then add maybe 2 inchs over that if turfing and 3-4 inches where you have flower beds. Make sure you stay 150mm below the dampcourse of any buildings. It is worth bearing in mind that clay never drains very well so if you find the area currently holds water for a long time ground drainage maye needed but thats an extreme case.