For his biting - which is why GSP are called landsharks; it is very normal. This thread will give you tons of ideas and other's experience with the same thing: Puppy BITING!!! Teaching Bite Inhibition
For socialization, this thread has an excellent conversation about it. Very experienced breeders and owners involved. rethinking "popular" early socialization
For training, this web site is an excellent beginning. Has articles and video tutorials. Training Positive | Dog Training Explained
Keep in mind your are working with a baby. Like all babies, the attention span is tiny. Keep training sessions very short and fun. Keep training treats small, you will be using a LOT of treats right now. After 2 days of training a sit, he will still needs treats - normal. Later you will be able to begin phasing out the treats.
Post where you are located, someone may be able to recommend a good trainer close by.