Welcome to the forums!!!
Litchi is great if you want waypoints but still prefer DJI fly overall. Everyone has their own opinion, see what works best for you, litchi does cost a fair bit though, I managed to buy on black Friday at less than half the cost with a coupon.
If your laptop doesn't handle 5.4k just use 4k (I only use 4k60) or unfortunately buy a better laptop to handle the video data. Could be the x265 or the 5.4k that's tripping your laptop up. Are you recording in normal or dlog or HDR? Try different setting for recording.
Try using your phone for editing as well. There are some amazing apps on android but none handle HDR.
Get yourself an external SSD or HDD and backup everything you think is worth keeping, I also have webspace and use that so I can access from anywhere. I save everything in a location folder and date/time them too as I return to places to re-film in different lights and weather.
What started off as a small hobby 12 years ago has turned into over 11tb of footage and that's with removing a load of stuff aswell