Well welcome to the site and he is just adorable. They food you can give a week or so to see if it gets better. We feed our pups FROMM Puppy Gold on the pink bag and our pups do great on it. I don't know how much you are feeding him, but sometimes if they get too much food that will make their poop soft. He should be fed 3 times a day for now until about 5 months of age. Try cutting back just a little on his food to see if that helps with the loose poop. Sounds like the breeder never took them outside so he is not used to that. Give him time and patience and he will figure out the potty outside thing. We have two 10 week old pups now and they know just what to do when we let them outside. It just takes time and plenty of praise when they do finally go potty outside. We always let ours outside when they are about 5 or 6 weeks old so they can get used to the grass and this helps with potty training.
One of our pups decided she didn't like the puppy food any longer and stopped eating it, so we switched her over to FROMM Pork and Peas, which all FROMM 4 star foods are an all stage food and can be fed to pups of this age. She is doing well on it.
Just be patient with him and he will learn soon enough. Another thing we use is cotton pads with an absorbent lining and water proof backing for puppy pads. They work better than regular puppy pads and are washable, plus the pups don't tear them up as bad, as they love to chew on every thing. Let me know if you want me to send you the info on where we buy them.