K64 can be plenty saturated, but you might find it helps to underexpose 1/3 stop or so. More likely, it's the instant film that is not saturated enough. You might experiment with different film types.

There are instructions on handling and loading Polaroid materials and a list of products they make at the Polaroid website. Also go to the Fuji website. You might find that the Fuji FP-100C is more to your taste, but I don't know how well it transfers.

The pack should just snap in, so it shouldn't be too difficult to load. Be sure to check and clean the rollers before inserting a new pack. Be careful not to pull the film too quickly and to pull it straight out of the holder, if you're getting undeveloped patches. If you don't get a white tab after pulling a yellow tab, you can open the holder slightly in subdued light and fish out the next white tab.