Should i start with Bloodborne?
As you may know from reading this thread these are my favourite series of games, so I may be a 'tad' biased but they are all superb. Saying that I would personally start with the DS1 Remaster - It's a slower game combat wise and does a good job of teaching the Soulsborne 'don't rush in, take your time' philosophy which will put you in good stead for the other games in the series. Bloodborne's combat is much quicker and I've known some people have been put off by just how vicious and unforgiving it can seem to a Soulsborne virgin.
Also i don't like games that are too hard, and i hear this game is really hard.
These games are very hard, and very challenging - but (and this is something that has been said a million times) they are fair. It's very rare that you will die from anything other that your own impatience or lack of experience of a new area/enemy. Put it this way, I don't consider myself a great gamer by any means and my reflexes are nowhere near as great as they used to be, but I've now Platinumed 4 Soulsborne games so that should show that they aren't just for the gaming leet.
Can you lower the difficulty either in-game whilst playing or at the start for an easier playthrough?
There are no difficulty settings.
Hope that helps a bit.