I would say capsule wardrobe could be something like this;
1.Linen trousers x2(1 dark,poss brown,1 light,ie cream/beige,look good under dresses)
2.Two dresses,poss empire line(Warehouse good for these,also Great Plains,Principles) can wear over trousers or alone.
3.Great fitting jeans,poss lighter weight denim.
4.Vests/t-shirts,plenty of,try Topshop/Dorothy Perkins/Marks and Spencer.
5.Two cardigans,poss one cropped,linen/viscose mix good for Summer,can be worn over dresses,vests etc.
6.Two skirts,again Principles especially good this year,also Great Plains
7.Ballet shoes(try New Look),sandals.
You could wear one of the dresses for the Christening with funky jewllwer(add that to list as well,Wallis good for this!
Hope that is of some use,and not too over budget!!