My feeling is that the dose of epson salt recommended is a good place to start but as we all know each one of us is different. Personally I changed the portion to less since I can just barely stand the taste and wanted to see if less would do the job. For me it did although in this case I'd been on The Master Cleanse for a week so that may have something to do with less being affective. As for the Sea Salt I remember seeing somewhere that it can be substituted as the morning oral enema instead of epson salts for The Master Cleanse (Altho' senna tea the evening before is still much more pleasurable).
As for the coffee enema use a plain water one first to get as much stuff out as you can first. I found it's easier to retain for best affect that way. Also helps to have the coffee a bit above body temperature (not too hot!). The main purpose is to help the liver release toxins so you want to retain it for a bit. Personally it relaxes me and I get a great nights sleep afterward. Kind of the opposite from what you would think a direct injection of caffeine would do.
Jay