I use the raspberry pi method for controlling all my devices.
the MPCNC has a Raspberry Pi 2. It runs Repetier Server Pro with a webcam. I don’t have any issues with the size of the file or how long it takes. it’s worked beautifully.
the MP3DP has a Raspberry Pi 3. It also runs Repetier Server Pro with a webcam. also no issues on file size up to 10-12 hour prints. I think the limit may be around 16 hours though as I did have a 20 hour print go south on me. but I’ve only tried the one file that large. but, I drop 10-12 hour prints fairly routinely and it works beautifully.
the laser engraver also uses a Raspberry Pi 3, this one doesn’t have a webcam but does have a 7" touchscreen. This one took more work to get stable because the laser engraver doesn’t have perfect software (yet). one of these days I’ll get a marlin/ramps board set up for it.
the (soon to be) lowrider will also have a Pi3 running Repetier Server Pro (until it proves incapable).
in all of these cases, I upload the gcode files from repetier host on the laptop, and trigger the machine start from the repetier web server interface. I tend to watch the CNC initially so I usually walk the iphone out to it and start the cut with the phone. Then I can walk away.