... I'll probably start with 1080p too. But want to be covered for 4K for future use as well....
Be advised 4k H264 is difficult to edit smoothly using almost any hardware or software. FCPX is faster and more efficient than Premiere, and unlike Premiere it uses Intel's Quick Sync hardware acceleration (on Mac), but even that's insufficient for truly smooth, fluid editing.
The hardware, software, acquisition codec and resolution used by Hollywood to edit feature films is often misunderstood.
Of the nine 2018 Hollywood films nominated for a best picture or best editing Oscar, none were filmed in 4k. Five were shot on film, five were shot digitally, one used film and digital acquisition. The film productions were scanned and digitally edited.
The digital productions were all filmed in 2k up to about 3.7K, and all used either the ProRes or ARRIRAW codec. The single exception was I, Tonya which had limited sequences shot in 6.5K. None were shot with RED cameras. None were edited at original capture resolution -- all were edited using essentially off-line proxies at 1080p.
None were edited in Premiere or FCPX or FCP7, all were edited in Avid.
The editing hardware was often laptops, not high-end multi-socket workstations. Obviously when they hand off to finishing, that typically uses a higher end machine for graphics, but we're talking about editing, not CGI or finishing.
https://blog.frame.io/2018/03/05/oscar-2018-workflows/
So this is a very different workflow and imposes different hardware editing requirements than 1080p or 4k H264. Hollywood editors actually don't need super-high-end hardware since they are often editing using a lower-resolution "off line" or proxy codec. Unlike H264, these editing codecs are not compute-intensive.
A few productions (none of the above) have recently used 2K or 4K ProRes acquisition and edited "on line", IOW using the camera codec. This enables screeners to see the full image potential, not some down-rezzed version. However this workflow is not widely used. Since ProRes is not compute-intensive even a mid-range iMac can edit 4k with good performance on FCPX.
For those of us shooting 1080p H264, almost any hardware or software will edit this with good performance. For 4k H264, almost no hardware or software will edit this with total smoothness, so you'll often need to create proxy files. Both FCPX and Premiere support this.
In FCP proxy files for 4k H264 are at 1080p resolution and take about 60% of the space of the camera files. So for every 1 GB of camera material, the proxies add about 600MB. Premiere gives various options for proxy size and codec.
