Good luck. Remember this is all new to him and from what you said he has been moved around and is probably a little confused and thinking is he staying here. Give him a few days to get comfortable. Don't baby him but try not to throw too much at him at once. Of course he is clingy he is probably human contact deprived. Make sure you leave him on his own as well so he knows you are coming back. You want to avoid him getting too clingy and hence develop separation anxiety. You will see changes in him all the time as he gets more at home.
I have free fed all my dogs if it works for him don't change it at least for now
A dog has so many friends because they wag their tails not their tongues.
R.I.P. Buddy 2002-2008 The best Mastiff ever.
Now owned by Clark the Crazy American Bulldog