In your green house you can plant the following in March:
Tomatoes and Cucumbers in a propagator.
Radish, Lettuce, french Bean, carrot, capsicum, beetroot, Aubergine. for later maturing in the green house.
The following can planted for setting out later
Courgette, celery, runner bean, Sweet corn, leeks and lots of herbs.
Any more questions ask away....I am currenlty reading abook on greenhouses...