Helen, you did say be honest.
I have the same age gap as you, dd now being 5months. There are good things - as everyone has said, having the little one on its own in the day etc, older one being able to help.
However, there will be hard times (unless you are wonder woman, which you may well be!) I find tea time especially hard, esp. now i am weaning dd. ds needs help with homework (yes, homework - even in year R!) and some days it all gets a bit much. As someone else said, plan ahead for tea etc.
When dd was about 3 months and I had got over the honeymoon period, I hit a really hard patch. ds was at home for Easter hols and I guess I actually started suffering from stress symptoms. THere were other things as well, ds and dd both ill (ds brought home numerous bugs from school and gave them to babes! Argh!) then I got ill and it all went tits up for a while.
But, it was temporary and things are sailing into much calmer waters now. I really love the age gap and woulnd't change it for the world, even though it was not really design but the way life worked out.
I think that as long as you are prepared for the tough bits (you seem to be thinking ahead etc!) I bet it will be wonderful. Seeing the older cuddle the younger for the first time, and every time, it is so special....
Good luck xxxxxx