Hey Annabel. You don't really have to do much with pumpkins, or you can fuss over them. To get more female
flowers and therefore more fruit, pinch out the leading growth tips once they reach a metre or so in length. This will induce more lateral growth and also more female
flowers. The females are the ones which have no stalk (LOL) and have a swollen embryo fruit at the base. You don't need to prune the
flowers, but you can hand pollinate if you want to give the bees a hand. Just remove the petals from a male
flower and dab it on the inside of the female while she is newly open and bright yellow. This is usually in the mornings too BTW. You can also eat the
flowers. Just raw in a salad straight off the vine or dipped in batter and fried. Same with other cucurbits.
If you water the vine, just flood the soil, don't wet the leaves, and do it in the morning so the sun evaporates the moisture on the leaves before nightfall. Wet leaves at night is what spreads the powdery mildew which killed them off last year.
Pumpkin are gross feeders and will take all the nutrient you can get into them. This is best incoorporated into the soil as compost and manures prior to planting but you can side dress around the root
zone anytime. Mulching will help the roots maintain a constant temperature and reduce water loss. Use a well rotted manure or old meadow hay or whatever organic matter you have available for this. Remember that they are an annual and the vine will deteriorate later in the season and be attacked by bugs and powdery mildew and whatever. Don't worry too much about that. As long as you have some half formed pumpkins by this time you'll get your share. The old vine is an excellent compost accellerator. Run over it a few times with the lawnmower and stick it in the compost.
Don't worry about the ants. They won't do any harm.