Ignis Stellaris (Starfire) - Warhammer 40K Space Marine Chapter

I am alpha-testing a Warhammer 40K app called Tacticus. It is heavily based on the only game I regularly play on my phone, a hex-based tactical RPG combat game called Rivengard. Playing as the Ultramarines makes me sad; I would rather play as my own Space Marine chapter, created lo those many years ago - the Starfire Space Marines.

Since the last time I read anything 40K was 3rd edition in 2000-2001, I fell into a rabbit hole on the 40K wiki. Fortunately, I found a whole 40K homebrew wiki with a very long article about creating your own chapters.