What type of portable computing device fits my needs?

I need a new notebook computer but I would like some advice on which type of computer would fit my needs best. Currently, I have a 2TB 27" iMac, an iPhone 5s, and an AppleTV. I download a lot of music & movies and stream them to my TV via AppleTV. I was considering a 4tb WD MyCloud to store my media in a central location but not sure if it's compatible with iTunes and/or how that process works. Also, will I be able to access my media stored on the MyCloud HD with both my mac and new pc laptop?

I primarily use my current laptop for downloading and streaming movies and music, video and photo editing, and surfing the web. I want something with 15" or larger, high quality display. I need to have enough RAM to ensure streaming media is fast and uninterrupted (No buffering) but I'm not sure about what I should do for a hard drive. My first instinct was to buy a laptop with a 1TB drive because I need the storage space but if I buy the MyCloud is that really necessary? I like the idea of a SSD but I can only afford a 128gb SSD. They're expensive but like the idea of it booting instantly. Is it worth the price?

The iCloud will meet your needs without any problems.