Skimming through that thread will cause you to miss a lot of really good information.
Guineas do not dig like chickens do. If you want your guineas to be able to do bug patrol in your garden, NEVER feed your guineas treats from your garden. You do not want them to develop a taste for what you plant in the garden. If you teach them to eat the things you grow, they will remember and seek those things out in the garden.
There are no opossums here, but there are skunks, raccoons, feral cats and Great Horned Owls. If you do not have a secure coop with your guineas in it at night, you won't have your guineas for very long. Your guineas may or may not make an alarm when they find opossums. I have watched my guineas scream their fool heads off as they followed a feral cat along the fence. I have also watched them stare quietly at a skunk or raccoon in a live trap. I have also have them raise a racket just because they saw me approach from a different direction than I normally come from.
I allowed my first flock of guineas to do pretty much whatever they wanted to and very quickly lost the whole first flock to Great Horned owls. I never allow my guineas to be outside their coop at night. I absolutely do not allow the hens to sit on a hidden nest outside.
I always recommend having at least 10 guineas so there are enough of them for their proper flock relations. If you do not raise your guineas with chickens they should not have any desire to interact with chickens once they are mature.
Good luck.