Go with your instincts. You won't be disappointed that way.
My instincts told me 3-4 years between kids. I talked myself into a 2.5yr age gap because of our life circumstances. It has been a struggle. I wish I had've listened to my gut.
However, you will get by regardless of the age gap. You deal with what you've got and you make the most of it. IMO it just depends on your outlook, as with most life events. There's no ideal time to have a kid, get married, study etc necessarily, only what works for you or what you make work for you.
All the best!