Hi Welcome to the forum.

You need to take things slowly and not expect too much too quickly.
With the food aspect I would feed what his previous owners have fed him at least for a while,if you want to change it do it gradually as not to upset his tum.
Put food down if after 20 mins,he's not eaten it pick it up and give it next meal time,keep repeating this.Dogs will not starve themselves.Don't keep mixing and trying different foods or you may end up with a fussy eater.

You will get there,it's a strange place,lots of different smells & sounds you also need to gain his trust.