Do not use a microwave.
I thaw mine in hot water, I fill a bowl, ut the rats in it, when the water cools, poor it out, fill it back up, and by the time it cools again, theyre usially thawed. I do medium rats though so yours wont take as long. Just remember to feel the rat for any possible frozen spots.
And dont worry about him eating the eco earth, unless he eats a bunch of it I doubt it will hurt him