IMO, telling the name and location of the master blacksmith and armorer is a spoiler. Then again, Witcher 3 is about eye candy and story not gameplay. So it doesn't matter much.
Posted 7 months ago. It's been patched. Now you can only get XP when the game intends you to.
Trust me, by my post about the armorer and blacksmith, those who haven't played the game won't know what I am talking about, plus they are not the only master craftsmen in the game world if you still consider it a SPOILER.
As for xp, don't rush it, just do the quests and you will level to max intended in no time without any grinding.
I never grinded in this game and ended up at level 40 at the end of HoS campaign. One more reason why I like this game. Other games like diablo, where you have to grind and only grind- I lose interest in them very quickly.
Edit: having the x% bonus xp from monsters trophy equipped and you get xp from all monsters. I remember leveling up after killing a dog 15 levels below me. This is tested on an older patch though.