1) It completely depends on the hamster - they are the first thing that Willow (Syrian) will attacak in her bowl but my mum's hamster (also a Syrian) avoids them like the Plague! Some Syrians don't actually like them - but some dwarfs don't either! Dwarfs are just more likely to take to them
2) Personally, I feed about half a teaspoon (so around 5 or 6) every time I refill Willow's bowl, which is about every three or four days. I wouldn't recommend feeding any more than this because, although they are high in proteins, they are also high in fats
3) To be honest, I wouldn't buy it - hamsters tend to like plain mealworms more so there's no point really
4) This probably isn't the smallest bag, but I found a 100g bag for a pound at Poundland - it's cheap and has lasted me more than two months! If Sweep doesn't like them then I'm sure the wild birds would greatly appreciate them and it's not a massive amount of money to waste anyway