I agree with Pete I would make the beds bigger say at least the length of all three of those you have constructed.
Re-the height of the beds because your plot is quite flat I would say it would be sufficient to have the walls one course high just to keep the soil in place.
If you want a more permanent wall lay the bricks on end with half of it above and below ground ans this should work fine.
This winter I think I would first set out the bed positions as you want them, rough dig them and leave them to weather over the winter months, leave the aesthetics until you have your beds finalised.
What you might find if you construct your edging first you might want to change your layout meaning all your nice work will have been in vain.
Anyways good luck with your plot it looks to have good potential!