Is it working?
 

Am trying my first ever batch and not sure if it is working or not...

I used 4kg of red apples which got around 2.5l of juice. I added a cup of sugar and 5g of bread yeast while it was still a little warm after boiling then left it in a room with temperatures of around 10*C over night. I couldnt acquire an air lock so covered it with a kind of balloon made from plastic wrap with a pin hole in it, hoping that it would inflate from the gasses to tell me it is working but not pop.

So its been 48 hours now between 10-20*C (night and day). It has a half centimetre of foam on it but the make shift balloon has not inflated at all, maybe because the bottle is half empty?

Is the cider brewing or has the yeast failed? I am at a decision to either add another litre of warm shop juice with more yeast, OR just wait and do nothing... am also wondering how on earth I am going to know when it is finished brewing?

If you are seeing foam, it's working. You really should have it at least 3/4 full. Too much headspace and air can get in there. You want all the empty space to be filled with CO2, not oxygen. Might want to poke more than one hole in the balloon but if the container is only half full, the CO2 might not be filling up the space yet. Not too late to add more liquid to the mix. Foam means it's fermenting.

Add some more juice to it, when the foams dies down, taste it. Give it a couple weeks. It's done when you get a slight buzz after drinking a glass.

Ok thanks I guess you are right, I will add another litre with a little more yeast for good measure.

So once the foam dies down, do I bottle and refrigerate it for the few weeks? Also should I filter or boil it after its finished brewing?

Definitely do not boil it! Or you will boil out all the alcohol you made. I don't bother filtering mine, the dead yeast is full of vitamins, good for you. I basically just make beer and the occasional bottle of "pruno" from fruit juice. Throw some yeast in with the juice and some extra sugar. Airlock and wait a couple weeks. Don't even bother with refrigeration, drink at room temp when it looks done. Maybe someone else has better advice. Just experiment with it. As time goes by the yeast will eat up the sugar, for a period of time it will taste very sour, let it sit until it tastes right.

Does it smell like eggs when you drink it? Coz mine does right now, just 48 hours after starting... hope itll get better before i have to try it.

That smell means the yeast is probably a little stressed. Either from lack of nutrients or some other unfavourable condition like temperature.
Don't worry too much, that smell will dissipate and probably be gone by the time it is finished fermenting. Some people sometimes add a little yeast nutrient to help avoid getting that smell. But I've been lucky, only ever had that smell on one batch and it was gone by the time it'd fermented and aged for a few weeks before I bottled it.

Could it be because I added too much yeast? I added around 4-5gs of bread yeast for 3 litres of juice, the apples were quite sweet and I also included an extra 1 cup of sugar so figured there was plenty for them to munch on.

Hope all will be fine.

Just leave it and don't even worry about it for the next 2 weeks, mark on your calender, 2 weeks from now, when to try another small glass.

Yes, it will be fine, let it be.