The Church no longer defines when one must arrive for Mass (I believe that there used to be a guideline of before the Gospel reading). The Church also has no *specific *law about leaving early although in general one should not do so until after the dismissal.
Arriving late and leaving early **without **good reason is something you should mention in confession and let the priest guide you as to the gravity of the sin.
A good reason to leave early might be something like suddenly becoming ill or feeling like you might be sick at your stomach or something like that… a pregnant woman who HAS to go to the bathroom and cannot wait another minute… a young child that announces they must “go potty” right away and you must take them out. Something like that. Just to get out of the parking lot first… that would be something to discuss with the priest.
Same thing goes for arriving late-- was it out of your control such as unexpected traffic or a wreck that caused a delay, a sick child or one that would not put their shoes on or get in the car or otherwise delayed you unexpectedly, someone in the family ill, etc… or rather was it without good reason and with a careless attitude towards Mass? Only the person in question could answer and should discuss it with a priest if they tend to be scrupulous.
These are merely examples. There is NO specific “rule” or “law” on this that is universal in the Church. Use common sense, if it is unintentional or unavoidable it is likely not sinful.
If you attend the Saturday evening anticipated Mass then yes, that fulfills your obligation. If you go to a Saturday morning Mass, it does not.
In general, yes. In any specific situation, ask your priest.
It is not a sin to refrain from the Eucharist at any particular Mass as long as you fulfill the duty to receive at least once per year.