Welcome to the new world of e-smoking Dan...a bit confusing at first but you'll get used to it soon enough..I'm using Njoy devices and some E-cig devices(testbed)..you're getting the best (RUYAN) and hopefully more reliable because that's what gonna help you in your aim to be a healthier smoker....
As for starters, you are in Heavy smoker range and very switchable(non-consistent) so any tobacco flavoring will help..try out regular or Flue-cured or even Combo(DIY version)..and you need high density or Extra-High(you need to test it out..get some e-liquid) , take it easy and don't overdo it as your device is automatic(no off button there..

)..first 1 to 2 weeks you might get some headaches and dryness of your mouth and tongue..drink plenty of water and mild green tea(helps to quench your parched throat or suck on a lemon flavoured sweets)....you'll explore more as your cravings dig deep to reroot you back to traditional smoking..that's why you'll end up with the device perpetually stuck in your mouth

..fight you will and you'll overcome slowly the old cravings(all that will take place within the first 3 weeks...or more)
I don't know much about Ruyan but what I gathered is that it is supposed to be the Rolls Royce of E-cigarettes but do keep proper care of your device as reliability plays a big role in your conversion.....Good luck Bud
