OP, if you are still paying attention to this thread, you're asking a biased group. The people at this site tends to go with whatever Apple has ordained as THE WAY. Right now, that's 1080p for video. Apple seemed to cling to 720p for much longer than much of the rest of the industry and right up to the point at which Apple finally embraced 1080p, this crowd argued passionately for 720p: "720p is good enough", "the chart", "I can't see the difference (so you can't either)", "1080p is just a gimmick" and on and on.
Then, Apple did embrace 1080p and that whole 720p argument seemed to evaporate overnight. No one argued about Apple's 'mistake' in going to a gimmick resolution, the chart, and on and on. It's always the same here: seemingly 5-10% offering objective input, 85%-95% arguing for whatever Apple has chosen as THE WAY
right up until Apple shifts and then the new THE WAY becomes the way.
Home video or not, you get ONE chance to record what will become increasingly precious movies over time. Like some others share in this thread, I've got home movies shot on crappy VHS camcorders, 8mm and on- even old silent reels. While it's great to have them on demand now, I wish I could take my 2014 camcorder back in time and reshoot the same scenes in with today's hardware. I'd love to see long-since gone relatives in rich clarity. Some dear relatives passed before it was easy to record sound on home video and how I would love to hear their voices again. One doesn't get a second chance to capture those kinds of memories.
So my answer is not the THE WAY answer. My answer is: if you can afford it, buy the best quality video recorder you can get. If that's 4K, then get 4K. The family memories you capture with it can only be captured now. You won't be able to come back in the future and re-shoot these memories at richer resolutions. If your TV or Apple equipment can't max out 4K right now, so what... down-convert it for what you can display but keep a master version for when the rest of your hardware catches up.
The day will arrive when Apple moves on from 1080p to 4K. In doing so, this crowd will go right with them and the "1080p is good enough" and similar arguments will vanish much like the "720p is good enough" arguments did. Then 8K will become the "gimmick", "4K is good enough" and the whole argument chain recycles
until Apple rolls out an iDevice that shoots 8K.
Since cost is part of your question, there are <$2K camcorders that shoot 4K. Maybe go in with some others and share the camera? If you don't need to shoot often, maybe you can find a local shop that will rent you one when you need it? Do searches for refurb(ished) to possibly save some money. Take a job at an electronics store with a good employee discount or find a friend in that kind of situation and buy it through them.