A tip to get jelly to set quickly, put jelly cubes in measuring jug, add about 6 tbsp of water, dissolve in microwave, approx 1 min. Add ice cubes and water to make it up to 1 pint. It will now be quite cool and set quickly. Sometimes I use frozen fruit to the trifle. Since this does add juice when defrosted, I usually make the jelly up to less than a pint to compensate. When poured over the sponge and frozen fruit, it sets quickly.
To get the hot custard to cool quickly, stir in the saucepan in a sink with cold water. Prevents skin forming and you can then just pour it over the jelly and sponge base when cool enough.
I would second all the Delia suggestions and Good Housekeeping books. Good to get you into the basics before being confident enough to try other recipes and experiment more. Glad you have found some Delia.
Ex Home Ec teacher here! Those are still my go to books. The recipes are well tried and tested. Get those under your belt and you will be fine.
Incidentally, home made shortcrust pastry is so much easier to handle than shop bought and tastes much nicer. Use plain flour and half that amount of fat. I use butter and lard, straight from the fridge or block margarine if doing vegan pastry. Often nowadays instead of rubbing in the fat, I finely grate it, dipping the fat in the flour to stop it sticking. Then just gently separate the lumps before adding the water, usually 1 tablespoon of water for every 50g of flour is enough, or a little more. Mix firmly with a fork, then test by pinching with your fingers and it should stick together. Gently shape into a flattened small circle with no cracks. Chill in fridge for 30 mins wrapped in cling film. It helps stop shrinkage. Careful when you roll it out, not too much flour which will dry it out. If lining a quiche dish, do as your mum did and bake blind with paper and baking beans, prick the bottom first. A good idea to chill pastry case again before baking. Place on a metal baking tray. Bake at 190 fan oven until pastry just starting to brown. Remove paper and beans a little before to allow base to slightly brown. The eggy filling is then cooked slightly lower at 160 fan oven.