Assessed practical double salt prep

here we go...
Making a double salt questions help?
We had to make a double salt involving ammonia, sulfuric acid and iron fillings.

Would just like some help on a few questions please,

1) Why is it important to add the iron filings to the sulfuric acid in small portions (to make iron (II) sulfate)?

2) How does the procedure make sure that the sulfuric acid is in excess?

3) How do you know that the ammonia (to make ammonium sulfate) has been added in excess?

4) Why will the percentage yield not be 100%. (As to this question I know the answer, basically that some will be dropped/spilt etc. But how do I phrase this for the marks)

5) What would my crystals look like? (Again, I know the answer but it's the phrasing I need to get right. I think I have to say hexagonal or something like this)

Thanks for any help
Credit goes to GC93.