Have a look at this wet film from a stool sample:
1) What parasites can you identify?
Ascaris lumbricoides (roundworm) ova, Hookworm ova, Trichuris trichiura (Whipworm) ova, Fasciolopsis Buski ova
2) Are there any parasites in there which are difficult to diagnose definitively?
Yes that big one on the left; the Fasciolopsis buski could easily be a Fasciola hepatica also. Local epidemiology at the area of acquisition is probably more helpful than wet films at discriminating.
3) What abnormalities might you expect on the Full Blood Count?
Anaemia due to the hookworm, eosinophilia due to any of the parasites present.
For a quick quiz on Ascaris Lumbricoides, click this link.