I want to make my own chapter and I would like some feedback and help to add more fluff. Here is it so far.
When the Titan moon was in the Warp and the first full
GK were off the last stages of training, they received a help signal from a convoy of Astartes ships that have fallen to the Warp chasing some Traitors. Since the convoy was with several Legions the
GK council decided to send a very small team with the new
GK to also test their potential and save the gene-seeds from possible annihilation of the Legions. The corvette found the convoy and organized them to return to the monastery but a sudden Warp storm made things worse and made them lose their way. In the following years-millenia the convoy drifted in the Warp trying to find an exit. In the way the
GK guided the Legios and pourged Traitors and heretics found in various places and planets. They also encoutered Loyalist forces lost in the Warp and found that they were not tainted yet. The new team had to adapt to the new situations with the Warp environment, limited supplies and loss of battle brothers and crew. The
GKs died in the battles and the Legions were almost decimated. However the guidance and legacy of the
GKs remained and new neophytes trained. Finally, after a very long road, only one Battle Barge remained, with salvaged parts from all the other ships and parts from some Space Hulks and tech found in lost Forge Worlds. The saved Mechanicus played a vital role in saving the crumbling ship.
The Battle Barge and the remaining force exited the Warp in the Purge of Jollana (913.M41) when the attack of Ahriman loosend the barrier between the dimensions. They responded asap to the battle of the planet and fought a furious battle in the Library, yet not in a vital place as the
GK were. After the battle they reunited with the Imperium forces. The Inquisition was suspicious at first, but after a long process it found that the team was pure. They could not become
GKs, so the Inquisition and
GKs given them the privilege to go to other Chapters or found a new one. Most of them chose to make a new Chapter with the name "Bronze Foxes", to honor their first Chapter Master. While they fought a huge battle in a Hell-Forge World, he was lost to a cavern and was saved by dragging himself from a fox´s tail. The liquid bronze of the soil stained his armor. After his emergence from the cavern he managed to find his battle brothers and succeeded to organize a defence and they were saved. After this battle all the battle brothers have painted their armor Bronze-Brass color. The remaining Legion
SMs went back to their homeworlds, yet still remained in contact with the new Chapter.
The saved armors of the lost
GKs were given back to their Chapter and the Bronze Foxes started a path to the far fringes of the galaxy to bring the light of the Emperor. They passed the Ghoul Stars and finally they settled their homeworld in the Eastern Fringe (Scutum–Centaurus Arm, Vulpecula constellation). There they foun a ringworld (Hey, the
40K has a Dyson Sphere, so I am not outside the fluff there

) inhabited by humans and helped them eradicate the emerging Necrons from the world. The ringworld is older than the Necrons and the Old Ones and the War in Heaven. The Chapter stayed there, as the mechanicus wanted to find the archaeotech the ringworld had. The armor will be a mix of Greek Hoplite and Monks with other bits.
So far I am at this point. I want to make the Chapter a mix of
GKs, Exorcists and Blood Ravens-Thousand Sons. I am also thinking of using a modified
GKs codex as a force construction but I don't know if this is possible by rules.
Battle cries:
"Improvise, Adapt, Overcome"
"Vir sapiens et fortis est et vir doctus robustus et validus"
I started building the army for Blood Ravens so I used the basic
CA and home a basic structure made, but then I followed the dark path of DIY Chapter.

I am new to the fluff and I am sure i have forgotten many things. Thanks in advance and if it not the appropriate palce, please Mr. Moderator move it where it is.