is that massively popular tutorials often stop being popular very abruptly, once you start charging for them. It's a fact of life I'm afraid - there are just so many free resources still out there.
Experience shows that a 'tiny' fee is just as much a deterrent as a not-so-tiny one, so that if for example you charge 50p for something, you may sell as many copies (or as few) as you would if you charged £1. It's not so much the small charge that deters people as having to go through all the faff of getting out a credit card, or even worse, opening a PayPal account. They simply can't be bothered, unless the product is unique, and sadly yours isn't - I found at least half a dozen very comprehensive free Maya tutorial sites with just a UK search.
The Google search page in your link uses your own name as a search reference, and that's not really what people will use.
As far as payment systems go, you might be well advised to try PayPal to start with - customers can pay with a credit card, and PayPal is an easy route to online selling. It's also a respected name in the business. That way you won't be committing to expensive shopping cart solutions before you have some idea of how the business will go.
Forget about protecting your work - there's no way you can do it so it's foolproof, and it isn't worth trying. Make sure you have a copyright claim clearly visible on the PDF, and get your customers to tick a box to confirm that they have read your terms and conditions of sale - one of which will be that your work may not be copied or distributed, in whole or in part, or placed on an electronic retrieval system without your prior consent.