[HELP] My first series box!

Today I decided to move away from regulated mods and try out a series... so, I purchased a Noisy Cricket!
From what I have been told, 0.3Ω - 0.5Ω is the recommended ohms. I've been building coils for about 2 months now and I've always used Kanthal A1 26ga×2 + 32ga Twisted Clapton wire. I know that dual coils with 4 wraps always comes out to 0.2Ω - 0.25Ω
Now, I've tried using ohm calculators to determine how many wraps with a specific wire and diameter but I can't quite figure it out. I plan on putting my Velocity RDA on my Cricket and use some Kanthal A1 24ga wire (dual coils) and try getting a 0.4Ω.
When I tried using the calculator last time I put all the information (I tried my best) and it told me how many wraps but when I built it. My resistance came out to 0.67Ω. Could someone tell me how many wraps I should put? I guess I'll use a 2.5mm or 3mm in diameter. Also, sometime I chain vape on my RX200. Is this unsafe on a series being that the batteries may get hot? If they do start getting warm, should I give it a break?
Thanks for any advice and sorry for all the newbie questions. I'm just trying to be as safe as possible because I've only used regulated mods in the 2 years that I've been vaping and never really bothered.