I'm not sure of all the ins and outs of the module... hopefully someone that's used it can chime in. You almost assuredly don't need the Java SDK, though. This is a PHP app and all the required code should be in the module itself. You may indeed need an SSL cert, though you can always contact tech support at PayPal to get a sure answer. It could be referring to some other downloadable API certificate from your Payflow account or something.