May be you should make some raised beds in pattern shapes have a look on google some good ideas on there, make sure you add drainage in the bottom stones or something. You could buy some cheap seeds wild flower - good ones in 99p shop -sprinkle on and watch them grow or some plants, fox-gloves are nice and self seed them self well. Maybe plan out on paper first you could use some thing like a garden hose to mark out shapes in the garden
Try the seed swap forum you could get some cuttings or seeds and some don't mind given them away to help others.
I thinking stepping stones or gravel going to the beds and to your greenhouse would look nice, assuming this would be placed towards the back. Either way, I would suggest from previous experience that you get some weed control fabric or simillar placed under whatever you lay so you don't have to deal with the pesky weeds later and have it ruin your creation! You could also use some mulch fabric in the beds to stop weeds here too. I used this site when I made some home improvements recently and managed to get a lot of what I need from them : http://www.qvsshop.co.uk/landscape-fabric-115-c.asp. Good luck with whatever you do and happy gardening.
Thanks Harry, was thinking of putting the greenhouse on right-hand side, there is a bit of a 'recess' at the end of the hedge, and thought It would tucking but still get plenty of light as south is in line with the trellis fence. Then I could build my compost in that corner too. My garden is an irregular shape as the top part used to belong the the house behind.