Liebherr re-gass

I have a Liebherr fridge freezer that was given to me with a faulty fridge.
Turns out it was low on R600.
I bought some gauges and R600 cheaply to experiment and see if I could get it going ok.
(I’m not daft and am a explosive area sparks so I know how to be careful.)
I don’t have the correct temprature scale for R600 so all I have done is fit a service valve on the low side and check the pressure while running which was in vacuum. I added enough R600 to make my gauge read about 2psi and the fridge is now ok.
Q1 what is the best way to get this spot on, should I vacuum it and weigh in the R600?
Reason I ask is that the low side pipe is frosting so I ‘assume’ its a little bit over? Or is that normal on an empty unit working hard?
Observation of the fridge temperature sees a wide range from -1 to 6 degrees, I was told as this is an old unit it dosent have a heater to defrost so it may work this way normally?
Lastly, this unit came from Australia, had an Aussie plug on it, but I don’t know if it was bought there? Will it be a ‘tropical’ unit if of Australian origin but made in Austria!
Had it on test for several days now and seems ok so I would like to start using it, any other chrcks I should make first?
Cheers.
Paul.