Garden Box Questions

I posted this in the Beginner's Landscape forum, but maybe this is a better place. (I live in PA.)

My husband and I are tackling a whole-yard project, complete with a garden box. We've built the frame, but now I have some questions...
Like, how do I fill it? I mean, obviously I'll have to put dirt in it, but do I put large rocks in first? Should I put a barrier between the dirt in the box and the dirt of my yard below? Is regular topsoil okay? I'll be growing flowers mostly, but maybe veggies, too. Can they be grown on opposite sides of the box? Or should they be separated completely?
I also have a ton of questions about which flowers work best together and for my zone etc... but I'll save those for another thread.
Here's a pic of what we have so far. Any helpful tips would be appreciated! Thanks for any help.

http://davesgarden.com/forums/f/containers/all/

The first item is called a "sticky" for it's valuable information regarding soil, amendments, etc. I know it's long but a few of us seasoned gardeners have read it a few times to absorb the good information. The wick is ultra important.

Have fun and report back with your successes.

LG, Looks very nice!
You can get many opinions, but I would not add rocks, just compost & topsoil. It will drain through the ground anf the elevation will give it great drainage. Veggies & flowers mix well, you don't even have to put them at opposite ends. Herbs too (there are pretty ones).
You don't want to mix plants that love lime with ones that love acid, or shade lovers with sun lovers, etc. You will have good, nutrient rich soil so you won't want to plant things that like poor soil. But you will have a great place for the vast majority of plants.
Hope this helps.
Dave

Thank you for the info! Yes, I'll check out the sticky, too.

The nice part of the sticky is that you won't be tested - thankfully!

Nice box. Dave (above) had good advice. I'm assuming you will be putting in a path in front of the box for access. I learned the hard way to put plastic or something under the path material to prevent weeds and grasses from coming through.