I'm just looking to get started with video, so my needs aren't super high at the moment. Short 10-20 minute videos. Probably 1080 and the maybe the occasional 4K. Is it necessary to go with the 27" 5K iMac? Will the 21.5" 4K iMac connected to an older 24" Dell display suffice? I realize the 5K will future proof things, but it's also quite a bit more expensive.