Cristian

Personally I go with not over thinking things. Use some basic math skills to calculate how many parts of this and how many parts of that combine for the total desired nic strength and pg/vg mix. Personally I then calculate 15-20% of that total and add that amount of flavoring. The flavoring end of things is going to vary widely from person to person of course.

I don't use drops as a measure. Way too variable and thus inaccurate. I use a graduated vessel of which there is a wide variety. A simple measuring cup is a graduated vessel for larger volumes though I don't advocate you use one. A graduated scientific vessel of desired volume would be best imo but there are a lot of things that fall between those ranges. For smaller volumes a syringe would be good.

It's not rocket science.

Very glad you are being cautious with the nicotine liquid. so long as you treat it like any medication or toxic chemicals in you house, you will be just fine.
not any help with nicotine testing, I've never gotten around to that.

using a calculator will help a lot with any mixing needs. 120mg nicotine to 18mg....4.5ml nicotine + 25.5 PG and/or VG = 30mls of 18mg

Here's an e-juice calculator link: http://www.todmuller.com/ejuice/ejuice.php

Hope that helps?

Just saying, you may want to move this thread to the DIY forums - that's pretty much the only place threads that talk about nic amounts that high are allowed.