If I'm outputting for the web, I often do long edge of 1000-1200px, 90-100 quality, and sRGB color space (this is important). Sometimes I'll go down to 80 quality. If I'm printing, I either hook the printer up directly and print from LR, or if I'm sending it out check and see what they want. Usually they'll want sRGB and JPG and I'd export at 100 quality. If you go to a higher end print shop they might also take AdobeRGB and TIFF files. Size depends on how big you are printing, taking 300ppi as the standard, multiple by the size of the print in both dimensions, and you've figured out your export size.
Now mRAW vs full RAW is a different issue. If you're after saving file space for your main files/archiving, my suggestion is to make sure to delete what isn't up to the level you decide you want. It takes some dedication and intention, but you can easily just discard the ones that you feel aren't great and save a lot of space that way. If you still have space issues, mRAW might be a reasonable way to go. For output to JPG, I don't really keep any of them around long term (ok, they just sit in the export directory until I get the urge to clean them up) since you have the RAW file and your LR library, right? And you're backing those up appropriately, right? You can just re-export them and get the JPGs again. That's what I've done as needed.