Is the card used to pay for the flights in your name or the company's?
I see the yearly price is $500-ish.
Is this for the card? Which card?
No UA premier status allows free lounge access in the US. Status on another *A carrier may allow lounge access (I'm not completely sure). If you are *G (or flying business or first), you'll get lounge access before a departing international flight. If you are Gold or better on UA (or flying business or first on UA), you should get access on all domestic connecting legs for an international trip.
If you are *G or gold or better on UA, you will get lounge access (on other *A lounges) in connection with international flights
As far as I know, UA doesn't have challenges except if you are already elite, there might be either a status challenge or a match (check other posts for answers to this).
4. Check UA's website for elite benefits.
5. Global services might get you regularly upgraded. Note, there are no free upgrades on international flights.
skipping TSA (or going through the pre-check line) comes only with either pre-check or global entry or nexus
On UA the only way to get status is to fly (or status match). Some airlines you can get a certain amount of qualifying miles by credit card spend.