Revell of Germany offers a conversion chart for Revell to Testors brand paints, and they intend to broaden it to include the Tamiya line in the near future. You can access it by going to Revell.com, then to Revell of Germany where you'll see a link to the chart; Germany Paint Chart.
If you have the time, paint4models.com is a comprehensive cross reference for many brands. It's a valuable reference, but it takes a lot of effort to navigate. I used to be able to use the search feature in the online version, but that no longer works for me, so I download it and scroll to find the info I need.
As for mixing, I also use the eye dropper method. I get the droppers at my local big box drug store. My mixing containers for small quantities are tattoo ink cups, which you can get by the hundred on eBay for cheap. I clean and save used up glass bottles for larger quantities and lacquer based paints.