Generally, there's no need to use FirmwareSender directly - everything you need is doable with makefile. So normally I would just run something like "make patch PATCHNAME=PatchNameGoesHere clean load".
FirmwareSender can be passed as env variable too, but I prefer to make a symlink in default path (Tools/FirmwareSender). TOOLROOT variable is set to empty string by default in recent versions of OwlProgram.
The requirement to use PLATFORM variable is removed, you can build patches with display without using it. Actually we'll probably have to reintroduce it later, but for a different purpose - to build patches for other MCU families.
"Template" is default path name value, typically you see it in one particular case - when you have mistyped "PATCHNAME" variable name. Other than that, there's been a lot of changes to OwlProgram in last few months, there's no point to troubleshoot its version from October.
I have no idea what's wrong with that USB cable, but you may be interested to know that serial MIDI output is enabled in latest development branch. Currently it just gets a copy of all MIDI output, but there are plans to allow accessing USB and serial MIDI separately.