For Punjabi there is Teach Yourself Panjabi not bad . For the language of the GGS try and find an old copy of C. Shackle's Introduction to the Sacred Language of the Sikhs it's out of print but just what you are looking for.
1)Ummm.... have you tried checking if your Local Gurdwara offers classes for kid's? There's usually elementary material there that you can use for a Small Donation.
2)Maybe get your Parents to help you out
3)If there's relatives heading to india, ask them if they can bring some elemtary Material for you to get started.
as for sites, there probably Are Some, maybe even ebooks, but i've never had the need so w/ a little research you may stumble upon smthing Useful.
i think that it is best to seek learning and answers to your questions about Punjabi here as there is a lot of wisdom here especially to those who have known Punjabi for so long. i think that the best way to learn is through experience and as a new learner it is best to learn from the experience of others that is why this is the right place to be able to address your concerns as there are a lot of members here who are more than willing to help you out. just be humble enough to seek advice and it will surely come.