Great ideas!! If you are wondering where to get the Royal Canine mouse... I've seen them at both Petco and Petsmart.
Here is a link so you can see what it looks like. Look for a white box.....
Royal Canin Starter Mousse Mother & Babydog Canned Dog Food at PETCO
I think Petco may have milk supplement as well...and Nutri-cal for puppies may help give him calories, nourishment and vitamins if he's not eating well.
Poor little guy...it sounds like he's had a rough life so far. 7 weeks is definitely way too young to wean a puppy. I've heard of breeders selling their dogs at 8 weeks of age and IMO, it's still too early.
Did the puppy come to you sick with coccidia?? If so, I'd DEFINITELY be calling the breeder. You shouldn't have to cover all those vet bills if a puppy comes to you sick.