Reel to reel tape questions!

Question

I have just aquired a reel 2 reel tape deck. I have found sources on the internet for blank tape but am a little confused by some of the options. Is the mil the thickness of the tape? I've seen 1.0 mil and 1.5 mil. Are there any audio quality differences?What does the "Special coating" on the backside of the tape do? Is it worth the extra cost?Any brands that are better than others? Can anyone suggest a good source?Thank you!!!!!!. Dancan't wait to get back to analog!!!!!