You cannot change the cable in LaCee drives.
I've used 512GB for a while now and all my RAWs are stored externally. However, just with normal stuff on the laptop and then the rather large Preview file I keep on the HD from LR, I've bumped up against a full HD a few times. Right now I have it back to 100GB free but I don't have my Preview file on it right now and that file is about 90GB as I choose to keep them as long as possible and they are all 1:1 with a mix of 5DSR, 1DX2 and D500 files. Last time I travelled I decided that for the trip I would have liked to only take the laptop and one extra external drive for backup of the RAWs. That would mean leaving the first import of RAWs on the laptop and the preview file. Therefore this time I went to 1TB to allow that possible workflow.
That all said I think 512GB is totally workable but I hit the threshold enough over the past few years that I went bigger. 256GB could work also but you'd have to be very diligent in keeping things off the laptop like larger video files and not travelling with a large LR preview file.
My MacBook Pro is not my main editing machine anymore. It was up until last year when I bought a 5KiMac and now use that instead while at home.
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I understand not wanting a bunch of extra dongles. But my point is the only dongle I think you and most others would need is an HDMI one. For all USB-A devices you can just buy a new cable and nothing changes. Sure it is another expense but anyone who can afford these laptops can buy a few $10 cables.
For those that like the SD slot, that would add an extra external memory card reader. I would say though that anyone using newer cameras with SD will now be using the faster UHS-II cards and the internal one doesn't support them. the internal one is so slow that I always used an external for my SD cards anyways.
I'm not saying I don't understand people's points about the USB-C ports but I think it is blown out of proportion. If Apple gave me the option of choosing 4 USB-C or the previous ports I would no question choose the new 4 USB-C as this is the way everyone is going now and in another year any new portable HD will be shipping at least with the extra cable if not a direct USB-C connector on the HD.
As to the iPhone, yes I can connect it either with the small tiny adapter I linked to or with a new cable or not at all as I've never connected my iPhone to my laptop in 4.5 years anyways.