You just paid top dollar for your iPad. I don't cut corners on accessories myself. The cable for outputing to your HDTV was designed by Apple and at a minimum, is the one I would buy. As to the wireless keyboard, I personally really like Apples wireless keyboard, but you can google wireless keyboards and find a plethora of them. If you check Best Buy and in the search bar enter iPad Accessories, you'll also find several options.
The screen is not scratch proof. So, you can scratch it. I tried a Zag screen protector on mine and absolutely hated it, so I took it off and currently my screen in naked. I typically take 'uber' 'super' care of my toys, so I'm not too concerned about scratching my screen. But, at some point, I will likely order PowerSupport's Clear film for mine. I really like the fact that PowerSupport film does not require solutions to be installed (it's a static mount film) and while you can get it in anti-reflective, it will (IMHO) diminish the readability of the larger screen on the iPad.
Anyway, just my .02 worth......