1) sure assuming they are compatible flavors it might turn out pretty well
10 mL of the 16 mg/100 mL juice plus 2 mL of the 60 mg juice would equate to 2.8 mg in 12 mL which equals 23mg/100 mL solution/mixture. Too much though for you, so .5 mL of the 60 mg juice in 10 mL of the 16 mg juice would give you 1.9 mg in the resultant 10.5 mL mixture which = 18.09 mg/100 mL so right at what you need/want/.
2) I've seen it postulated by others that TH can or does have something to do with nic content, but I doubt 16 vs 18 mg juice would have much of an appreciable difference. But give the mixing a try and report back, I'd be interested to see if it does!
3) TH has something to do with PG and VG mix too I think I've read here so what is your 16 mg juice ratio?
Carbon