You could substitute some of the flour for wholemeal flour, it will give this a more nutty flavour. Do not add any salt as the instant potato will have plenty in it already. Just sample the first one you make to check the seasoning. Make sure you chop the spring onions very finely, and don't forget the lemon juice! Take care not to make these too large if you want them for starters, and when you flip them, press them down so that they are not too thick.
As for toppings, well I use the traditional sour cream, smoked salmon and capers with a little dill and lemon to garnish. Cream cheese also works well, and you can also add little slice of red onion if you fancy. Otherwise go for it!