Position (1st, 2nd, 3rd) is determined by the order in which the loans were recorded, unless a subordination agreement was recorded (the purpose of which is to change the order).
You can get title insurance by contacting a title company. Note that some may be hesitant to insure you, though you can usually get around that by excluding insurance from any lawsuits resulting from the trustee sale itself (title co’s are worried that perhaps you colluded or did something illegal in obtaining the property and don’t want to take on that risk).
Never had any issue getting title insurance when I have resold… unless of course there remains an outstanding title issue (like a valid loan or lien) which of course needs to be cleaned up first.
You don’t really need a full prelim. I know quite a few auction investors who have their title co lookup loan positions for them… but note the title company won’t bail them out if they give bad info.
Have not found ANY good books on buying at auction.