Yep, reckon 99% of the time you won't notice the difference. I haven't noticed the difference before, but if you are afraid of losing information, then don't use compressed NEF (storage is relatively cheap anyway - but if I was running out of space on my only card, I wouldn't worry about using compressed NEF)
Haven't noticed any difference in processing time.
Take a look at your manual - it will tell you the 'typical' file sizes of the different modes and you will see that Losless compressed is smaller than uncompressed by about 20-30%. The estimate the camera is giving is only an estimate as the actual size of each file depends on what the image contains, and I guess the estimate it is giving for lossless compressed is assuming no savings in size.