I am glad to see I am not the only one asking myself the same question.
I left a 3 year gap purely because I think it is easier if the older child understands, I even get some help from her every now and then! On the other hand, the adaptation is a bit tricky sometimes, a fine line between cuddling and smothering...
I believe there is no right and wrong answer, but I guess my advise is to follow your gut feeling more than anything else.
Good luck and enjoy it all! no matter what, it will always be exhausting, even when it is a walk in the park!!!