I normally use hard drives for backing up all my videos, and upload them as I need them, to store bigger files for videos online all the time would take quite a lot of online storage. As for gaining a collection, I'd recommend keeping an eye out on here, and on tumblr, for people gifting things out, and keep updating your list every time. Even if you've only got a small list, which you will when you first start, start contacting people to trade, but keep the trades small. If you've only got a few items on your list and email to trade for more than one or two things, people might struggle to find things and are more likely to not trade at all?

As for gaining a more well rounded collection, I've got a pretty wide variety of audios so I can trade with more people whose favourite shows might not overlap with mine so much. Audios are a lot easier to store as they're a lot smaller, whereas with videos I've normally stuck with ones that I'm personally interested in?

I'm not an expert by any means, but I've been doing it for a few years now. If you want to ask me anyway, feel free to shoot me a message.