Firstly don't panic! Secondly remember Alfie is still a pup and there's a fine line between not enough stimulation and too much! Keep things nice and simple, keep his recalling happy and fun, same with his stay or sit, let him enjoy his life as a puppy and then as he ages more towards 8 months ask more from him. His recall and stop is the most important thing he needs to learn, you get that instilled and this will hold you in good stead for the future, he'll never forget it. All breeds go through the 'teens' where they sometimes switch off or choose to ignore you for something they think is better or more interesting, if you find this happening then go back a step and work on the problem area before moving on again.
I can't help with books I'm afraid, too many people with conflicting advice and it would be up to you to decide which one you think would work best for you and your dog. Common sense goes a long way in training a dog, think why, how and when things went wrong if they do, and you'll be able to rectify the problem or seek a trainer you can work with.
If you want to go down the working dog route and follow a good trainer of working dogs then I can highly recommend any books written by Joe Irving which can be found at Amazon for a good price or maybe even eBay! But my advice to you is if you want to use a book, please buy a book by ONE person and not several as they all do things differently and this will just confuse you
Sandy

Rather contradicted myself over the 'not helping with books' there didn't I