DLC can be done after you defeat Vicar Amelia, an important story boss. However, most recommend you did it towards the end of the game as otherwise its difficulty might be too great.
One thing that I did not mention: regain. When you get hit, you have a small window of opportunity to re-gain your health providing you hit an enemy. Used wisely, this save a lot on healing. Use unwisely and it looks like you just committed suicide.
And if you are a filthy casual like me, the guidebook is superb ☺ Worth getting in any case as it's a lovely book.
Yes, you should get it.
Bloodborne is not a hard game, it is an unforgiving game. "Git gud" is actually good advice because anyone can get it and be awesome at playing Bloodborne. I have about 2-3 hours to play per week, am a filthy casual, and I finished the game no problems.
The guide book as well as the wiki are very good resources to have.
Oh and this sub is full of nice folks that will give you advise and help you in-game if you have PSN+…
The (one true) wiki is your best bet if you want accurate information.
The guide book is superb, very descriptive, and useful without too many spoilers -- Clearly, they do tell you everything but in a way that allows you to stop reading the bits you do not want spoiled. Oh, and you get a cool PS4 theme with it.
The fan-made map is okay… The maps in the guide book are much much better.