Finally reached a decision to go for no4 ... I think 
After alot of thought now we have decided dh would like to go for it asap whereas I'm wondering whether to start trying at the end of the yr as it means if I conceive straight away the little one would arrive around the same time dc2 starts school.
The first three are fairly close in age all under four when dc3 arrived and I found things easier when dc1 started school but on the other hand it would be a bigger gap still not huge but bigger than the rest
Any wise words and opinions appreciated.