Saddam
If you're in the UK, full fat soft cheese = Philadelphia. You can also use a generous spoon or two of lemon curd for the topping instead of crystallized lemon slices.
If you whip the egg whites well enough you will get a fluffy texture. If you use less or don't whip a lot then you will get a denser cheesecake. Tastes vary.
The amount of gelatin stated in the recipe was not correct when using sheets of gelatin. I would suggest you follow the instructions on the gelatin packet on how much to use for a firm set for about 500-600 ml of liquid, and use that along with the suggested amount of water.
Very good end result, cheesecakes are great!