Viki's video platform is in html meaning you don't need Adobe Flash, this app is still used by other websites though. I can tell you I even subbed from a tablet with a keyboard. A laptop is certainly more convenient because of a better keyboard and if you use photoshop etc. programs. To write subtitles and segments does not require a high tech machine, but sound quality is a plus I would think if you need to hear the said. If you plan to contribute a lot, a pair computer glasses to reduce glare is a good idea. Also something that won't get hot easily if you have it on your lap.
Storage capacity is probably secondary but processing memory size is, 4 gb is rather limited when you work with several windows or tabs open if not it's just fine.