Keep in mind that a set of gauges will not make you an auto A/C expert. There are a lot of other tools needed to work on an auto A/C. If there is a leak the source needs to be identified and corrected which can mean a $200 leak detector or yellow glasses and a UV light.
To work on the system you need to evacuate the system, saving and filtering the R134a for reuse.
To verify you need to pull a vacuum for 30 min and have it hold the vacuum.
And to fill the system it's filled by weight.