I'd say it would be hard work if you have a newborn and a toddler. Consider also you'll be PG when your LO is still very small, learning to crawl, not sleeping as much etc so how will you feel during pregnancy chasing round after your LO and not being able to rest etc when you need to. Remember how you felt in your pregnancy, especially first tri which is exhusting in itself. Then the later months when big and about to drop.
Also it puts more strain on your body having children close together and not having a rest time (iirc they say a year isa good time to allow your body to bounce back fully from pregnancy, labour and feeding etc). You have been drained of nutrients and goodness knows what else by your baby during pregnancy and will continue to provide everything for your baby for as long as you breast feed. Chances are you may not conceive when still breastfeeding as often women don't have periods or ovulate till they stop breastfeeding. Your body needs to be allowed to recover and get back into shape to be in the best condition possible for trying to concieve and carry a second baby.
I've cared for 4 children in one family and they are about 2 years apart in age on average. That was close enough IMHO. A good break between and the mother gave her body time to recover from one pregnancy before trying again for the next baby. Each child was old enough by the time the next came along and their mother had time to each of the new arrivals before the next came along.
Also remember that how your baby is, isn't how the next will be. Pregnancy wise or once born. You may have an easier pregnancy, maybe a tougher one. Maybe the next baby will scream the place down from colic and exhust you. Consider how you will cope if you have a demanding baby and also a toddler running round. Do you think your toddler would be left out? Not have as much time spent with you as they might need because you are with a new baby a lot.
There are pros and cons to having babies close together. I personally don't think I'd go for them so close simply for my own body and also as I want to enjoy my son as much as possible before having another. They are only small for such a short time and I'd rather be able to zip around and spend time with him for a year before thinking about the next. 18 months, 2 years is a good gap as children will be close enough in age but far enough apart to allow each child their own time before the next arrives.
End of the day its what you feel able to do and what you want to do and what you feel is best for your child and future children. See how you are coping in a few months and then consider things again. You may feel very differently then from now. If you want 3 or 4 so close togther then good luck to you. Its bloody hard work with four kids 2 years apart, I know that.