You could do part LME and part DME and you could use all DME but it won't be the same amount as the LME. Here is a formula on how to convert a recipe that uses LME to DME and vice versa:
LME to DME * 0.89
DME to LME * 1.10
If you're doing part DME, I would take the 2.4 lbs of LME you would be subbing for and multiply that by 0.89 to get the amount of DME to add.
I started doing extract kits and they all came with 5 oz of corn sugar to use added to a cup of boiling and cooled water for priming at bottling. I've found that 5 oz is a bit much for 5 gallon batches as most of my beers ended up way too carbed. I've since been using around 4 oz added to a cup of boiling and then cooled water and seem to have much better results with carbonation.
The grains are definitely only steeped. You want the water temp you are steeping at to be around 150°-160° F and the grains are usually steeped for around 20-30 minutes. You do not want to let your water temp get over 170° or you can release tanins into your wort so do not boil your grains.
As for the spices, I would suggest removing the cinnamon and ginger at the end of the boil but this is a matter of personal preference. I would think you would get overwhelming flavors by leaving them in the primary (especially from the ginger) so I would recommend taking them out before racking your wort to primary.
Hope this helps and good luck in your brewing!