Instead of whipping cream powder, you could use 300 ml whipped cream plus icing sugar to your sweetness, whipped to soft peaks. Then proceed with remaining steps.
You can replace half the quantity of whipped cream with equivalent quantity of custard, ie. 1 to 1 1/4 cup of thick and smooth custard should do.
I added the strawberry and it's juices and it seemed fine. If you feel there is too much liquid, you can sieve the strawberry puree and use.
To make the dessert a little healthier, you could substitute half the whipping cream with strained yogurt or sour cream.