I think it's OK to cut down a bit. But if you are wanting to only take in 1800 calories you can take 2300 as you roughly burn off 500 calories whilst breastfeeding.
I think eating healthily is your best bet than outright dieting. I'd also make sure you do get your sugar levels as breastfeeding can be tiring and depending on the age of your baby it might really drain you.
But it's completely up to you at the end of the day. I just try and eat healthily and have my usual amount and have lost nearly a stone in 2 months.
I have only just weighed myself after the birth of DS nearly four weeks ago. It was a bit of a shock. I am eating pretty healthily and certainly a lot less than when I was pregnant anyway so I am going to just carry on like that for a week and see if I am losing any naturally. If not I will cut down and start counting calories but not too much. I really hate being this over weight and I can't fit into any of my clothes!