Ordering bulk CDr / tape depends where you're located and how many you need. Best is to aim for quality, not cheapest. Last time I ordered bulk tapes, I went for highest price what company would offer. And you can clearly even see it. Probably meaningless for a lot of people, but simply thickness of magnetic tape varies greatly. Cheaper the tapes - thinner the tape, appears to be rule. During time it stretches and is potentially damaged etc. Tapes I recently got, even if being chrome C-30 and C-45's, they look almost like C-45 and C-60 since magnetic tape appears to be thicker and making the reels look contain much more tape than they actually do. And occasionally - as opposite, you get noise tapes where you think it can't be more than C-10 since there's barely tape inside the shell, yet playing time appears to be 20 mins..
Tapeline in UK is probably easiest European tape deliverer at this moment? They are ready to offer anything from cheap bulk to nicest chrome, cobalt or special tapes. Ain't worth saving in wrong place.
Friend of mine ordered bulk CDR's from... Malaysia or whatever. They were dirt cheap, but c. 1/3 worked after burning and even they started skipping in few weeks. If you're going to charge people money, then it's best not to save 0,1-0,5 per unit to sell them garbage, but go for best quality since price difference ain't that much it would affect intended retail value.
Contact mic captures sound from direct contact with object. Not from air. It's good for things like metal junk recordings, where you need to capture sound of metal - not all the surrounding sounds. Sometimes also easier to control unwanted feedback etc. Traditionally for example cheap piezzo contact mics have very narrow and distinctive sound. It can be good, but can be also limiting if you aim for something else.
Clean loops? Not sure what it means as I don't see context where its used. But I would assume for example smooth well running loops, where there is no clicks/pops/glitches in "seam" part of loop?
I would think saying length of tape is good if it's something out-of-ordinary. Meaning 10usd tape, you assume you get the album. Not the C-5 tape single. I don't think anything from c-30 to c-60 is utterly crucial to mention, but I think short tapes would. First of all, perhaps not even make them unless there's proper reason.