I wonder if you guys can help me?
If the corp has an asset and it has a few advancement tokens on it, I assume when I install a new card to take its place I trash the advancement tokens along with the card?
With an asset card like Pad Campaign, can advancement tokens be used to rez it, and if not do the advancement tokens go back to the bank?
Not sure what you mean since Pad Campaign can't have advancement tokens. But in any case make sure you make a distinction between advancement tokens and credit chips. They are printed on double-sided counters for convenience, but they are entirely separate objects. When you take a credit token from your stash and then put it on an asset as an advancement token, what you are really doing is returning a credit token to the bank and taking an advancement token from the bank. The advancement token no longer represents any kind of money.
When the runner accesses R&D do I just show them the top card? They then decided if they want to trash it; providing it has a trash cost. Then if it's not trashed, place the card back on top of R&D?
Correct. Also note that the Corp can't tell the difference between a card that the runner chooses not to trash and one that the runner cannot trash. The runner should avoid giving away that info when they look at the card.