I use the same as Mr. 2wheelsx2. I would use Eheim Ehfisubtrat pro but it is soooooo expensive. Matrix seems to do a fine job at a much lower price. I used the Rena Stars which are a porous ceramic material in the shape of a star which is well rated too. I put most of my bio media in a bag and then its super easy to clean. Just a quick rinse in some tank water and you are good to go.
Yeah, bag your media. Makes it easier to rinse vigorously too. Since there are 3 baskets, I'm not afraid to rinse one of them under full tap pressure when they are particularly dirty. If you have them bagged, you can even only do one bag at a time. Plus the bag themselves act as filtration material too.
Nope, it's not necessary for the Purigen. But in a bigger tank (especially if your tank is 24" or wider) water clarity can be a problem. But you can get away with all potscrubbers if you like. I don't like the fact that the potscrubbers are light and I only put them in the lowest basket.