You can mark the areas now but I would wait until the grass starts growing. If you fill now you might smother the grass. I know you're going to do it now anyway. Just be sure you see some of the grass sticking up through the sand.

Look for landscapers. If they show up with a bobcat or a skidsteer, send them away. Real landscapers use a tractor (big wheels on the back) with a box blade on the back. Unless there is a fence, trees, sprinklers, or concrete involved, a professional will be out of there in less than an hour.

A friend of mine used Sonrise Landscaping for her home. She had a drainage system put in her back yard. She seemed pleased with them. Here's their website:

http://www.sonriselandscaping.com/