My DD's are just under 18months apart and I love it DD1 is an fantastic little girl so I have not had any troubles with her and DD2 while a big mummy's girl she loves her big sister, they play really well and DD1 likes to mother DD2.
I would like to wait till DD1 is close to starting kinder before we start trying for #3. That way I can give the new bub some one on one time like both my girls got. In saying that I am already feeling that want to start trying but with a holiday to Vegas planned for May I will be waiting till after that at least.