Read the completed Novel first

I started the novel on the day the drama released, and completed it before starting the drama. And today I completed the drama, and my conclusion is that it is very different from the book. At first I was disconcerted by the differences but I eventually changed my mindset to see the drama as simply being 'inspired' by the novel. That way, I got to enjoy them both without constantly distracting myself with the gaping differences. I'm now eagerly looking forward to part two of the drama.

A spoiler on whether novel JCY had a concubine:

Jiang Changyang did take a concubine in the book but it was in name only. You could say, technically, Mudan got a concubine on his behalf, lol. Mudan was going through some difficulty (all instigated by that rotten Liu Chang) at a time when both her father (and a couple of her brothers) and JCY were out of town, and this woman helped her in some way and wanted the favor returned. She worked in a high-profile brothel (or a gambling house or some such place, can't remember the exact details) and wanted to be redeemed, and insisted that JCY should be the one to do it. Mudan agreed to the favor, and JCY redeemed the woman when he returned. It was all lowkey (but the Emperor did find out, IIRC). She never lived with them but relocated to the hometown of JCY's mother and stepfather. 

I'm confused. I just started reading the book and she talks about being reborn in this body with all its memories...... Did Mudan originally die and someone else come into her body?

 Sheriziya:

@LucianYaz  Ah, I had totally forgotten about that. If I remember correctly, she first lived with Pan Rong and then came to JCY's place on Mudan's suggestion because Madam Bai was pregnant and having some difficulties?
Because neither one really saw her as a concubine, I totally forgot about it :D
In the series it's quite different though. But the whole series is more "inspired by" instead of a transformation from novel to series :D

Definitely 'inspired' by. I encourage people to do both - read the book and watch the drama, as both are great in their own way.

 LucianYaz:

It's not explained in a satisfactory way (just hints here and there) but it does look like the original Mudan died and this other woman from the modern world was reborn into her body, and gained all the memories of the original Mudan. This rebirth has no major effect on the story or plot, and could've been left out entirely, imo. Her knowledge of modern things does help her in some ways but not enough that it needed to be included in a such a scanty way. I felt that the author should've either made more of the rebirth angle or just left it out entirely.

I agree. If she had left it out, it wouldn't have made any difference. At least that's the way I feel it.

 Nope:

My guess is that it is meant to explain her personality shift before and after her 'relapse' and near death experience. But honestly, nearly dying can change people enough, that it wasn't necessary.

I agree :)

 Nope:

I'm on chapter 10, is Pan Rong JCY?

No, Pan Rong is Madam Bai's husband. Totally different person.

From chapter 10:
Princess Qinghua pretended not to hear, continuing to laugh and chat with Liu Chang, her body shaking with mirth. Pan Rong, stroking his chin, stared at Mudan and said with a smile, “Zishu, is this your wife? It’s been so long, and she’s blossomed beautifully. You’re a lucky man.” 

Pan Rong laughed again, “Brilliant! Next time my wife scolds me like that, I’ll know just how to respond.”

 Nope:

This was why I was confused becuase he seemed very interested in her, and came to her defense....so I wasn't sure what was going on....plus JCY still is a no show in the book...

He will show up soon enough :D Just wait and read on. :D

You'll also soon find out why Pan Rong is interested in He Weifang :D

 Nope:

Yep, I already know.  JCY in book in completely different....so far.

You'll find there between the novel and the series there's shiploads (and no, that's no error on my side :D ) of differences.
The series is inspired by the novel instead of it being a transformation of the novel :D