1 The recipe you have is for short-crust pastry, but yes you can use all marge or all butter. Lard is animal fat but you can buy vegetable fat instead. The half and half makes it "shorter" if you like.
2 Puff pastry has lots of layers of pastry and butter is a devil to make and best got ready done from the frozen section of the supermarket. You should be able to get shortcrust pastry there too if it all gets a bit too complicated.
3 You could always do a crumble topping instead of a pie topping. Or a blackcurrant sorbet is v nice.