Editing, and I need YOU!

So, i am editing my first ever story Secrets & Lies.
I wrote this story in 2008 starting when my daughter was 6 weeks old. It took me a year.
When i finished it my dad printed and bound it. It hadn't been edited, it was very rough. Everyone who read it said it's a great story.
I read back over it about a month after i'd finished and well, it needed a lot of work!
I was really bad with head hopping! one sentence was in the heroines head, the next from the hero's father etc :S
So, five years later i am editing it.

I have started with the first 6 chapters, deleting head hopping, making scenes in one person's POV.
Upping the tension by deleting all the obvious 'hints' to character's backgrounds.
And, i have done research. When i wrote it, i created a fantasy land in an unknown time. It was easier to create my story. Now i want to solidify it, ground it somehow, and i have chosen a place in the Hebrides, in around 1100 AD.
So lots of research, about clothes, food, names, travel etc etc..

So my question for you writers, both published and unpublished. What do you tackle first on your first edit through?
POV?
Inserting place names and history?
Changing some of the plot line? Character motivation?

There seems so much to do, i am a bit overwhelmed where to start!! So your help is greatly appreciated!