For your next batches:
1. Use more water to steep your grains, then divide it between two pots if you can't get it all to boil in one pot.
2. Steeping is not a terribly temperature intolerant procedure. You won't change it much between 120 and 180 degrees. The main reason to keep it between 150 and 155 is practice for all grain because the conversion of the starch to sugar is temperature dependent.
3. DME isn't as particular about when it is added as is LME. Your wort should be boiling when you add it though. It dissolves better that way.
4. You don't want to boil off so much water that you get sludge. As your wort boils, add water to keep the level up. That should help prevent the scorching.