Here are some photos of the Thunderhawk I built on commission:
http://www.dakkadakka.com/dakkaforum/posts/list/349852.page
Predator or land raider sponsons/turrets work just fine. I magnetized the mounts for easy access and so I didn't have to worry about gluing a moving bit in place.
I sculpted my own intakes and exhaust vents, so I can't help you there.
Build the top cannon last, and build it in a size that looks right. The one I built is about 6" long and made out of .5" polystyrene tube with a step down for the end of the barrel.
Use Valkyrie missiles and magnetize them. You get two in a box. Otherwise you can grab yourself some aircraft model accessory missiles from Tamiya or other model company.
Don't glue yourself to the model and you'll spend three times as long on the last 5% of the model doing the details than you will on the other 95% of the model. This is a good thing, the details make or break a scratch build.