Matt: Thanks for the post and congrats on your upcoming hike! That's exciting!
Your timing is perfect. Although you'll find snow in July, it will quickly disappear by July 15 or so and will be replaced with mosquitoes.
The toughest snow for you will be in Northern Washington. It's not clear how much experience you have in using a map and compass (or trekking through snow).
My best advice: verify where you are every 10-30 minutes (depending on conditions).
The biggest navigational error backpackers make is only looking at their maps when they're lost. By then, it's too late.
Look at your map when you know where you are. Mark the spot. Then look at the next couple of miles on the map and try to imagine how the terrain will look like. Example: "There will be a creek on my right and a steep mountain of my left." That way, if you find that there's a creek on your left, you'll know something is wrong. Since you've checked your last known spot, and you have a sense of how many miles per hour you're walking, then you'll have a good idea where you are. By checking every 15 minutes, you can't be that far off.
When you see snow up ahead, be especially vigilant and meticulous of checking and re-checking your location.
If you haven't done much navigation, practice it in the next couple of weeks before you start.
You sound ready and I hope you write back to tell me how it went!
And remember, as a Sobo, when all else fails and you're totally lost, hike south!!!!!