In the quest ‘Berangar’s Secrets’, how to go see Coleman if he is dead

Don't neglect alchemy. There are fights that are incredibly difficult without potions that become easy-mode with the right one(s).

Also, there are several points in the game where you are required to make a choice, and this will affect conditions later on (a later fight may have more/different enemies, for example). None of these are game-breakers, but you may want to consult a guide if you don't mind spoilers and feel the need to make the "right" choices.

(Here's one from GameFAQs, for convenience. I'm sure there are others out there.)

They are sensitive to fire, using Igni to ignite them works pretty well. You can use Argentia oil on your silver sword if you have the material to increase your damage.

Be careful to never engage more than one of them, they can't move so you just need to position yourself well. There is also a named archespore in the swamp (Coccacidium) which can easily kill you if you're careless. It looks very similar to an echinops and can spawn in several locations. You'll get a trophy for killing it. You might have to avoid that one until you leveled a bit if you're having problems, but you should be able to kill the normal echinops.