
You can read the novel here: https://exiledrebelsscanlations.com/novels/grandmaster-of-demonic-cultivation/
I think it's better if you start from the very first chapter to kind of get the feel of the novel and to enjoy it to the fullest, I guess? I think there's some parts from the novel that weren't exactly illustrated in the manhua

Novel and manhua are almost the same as far as I can tell. Anime skips or alters some scenes mostly for censorship. And the second season from anime is diffrent from novel or at least it feels diffrent to me and there are couple of scenes I wish weren't altered. Live action differs from the novel most. The ovear all story is the same but it's also completely diffrent from the novel and as far as I know it's only loosely based on the novel. I have only just started watching it and it's so diffrent from the original almost from the start. From what I can tell most of the impotant scenes are mostly the same. And most important thing is that at least in the live action there is no romance between Wei Ying and Lan Zhan they changed it to bromance.

I too agree with you.
From what I've read and seen manhua is the most similar or rather equal to the novel in every aspect.
And the live action doesn't even utter the word gay and hence changed some things like who Mo Xuanyu has harassed(?) and the dear friend's hand in the beginning has changed into saber spirit. But the rest of the story is pretty on point and they did include most of the subtle actions and eye contacts and dialogue of Lan Zhan and Wei Ying. And even though its really subtle we can see that they both love each other.
AND the anime is just literally another story with the same plot but do say that Mo Xuanyu is gay and so the first season did follow the novel but the second season was completely different and they had changed many scenes. But the animation is super cool.
Personally, I prefer manhua after the novel.

Ah! But there were scenes in the anime that aren't yet in the manga like the giant tortoise killing thing, there was even a flashback of the archery match and wen chao destroying cloud recessess and yunmeng Jiang sect and even the whole Wei wuxian transformation thing..did they take that from the novel...will they be adapted/made into the manga!!??

In the anime flashbacks come at diffrent places than in the novel or manhua. The turtle flashback was originally mutch later... so yes both those scenes are in the novel and I loved the original scenes better because they were edited, the tortoise scene was much better!!! I was disappointed that it was changed ever so lightly ╥﹏╥
Where can i read the novel. What chapter should i start?