The overall luminosity isn't going to be that bright, but you may want to be able to do long exposure which may require an ND filter.

As for fumes, there generally isn't ash in the case of surface eruptions. It is mostly just noxious gas (ie, "clean" air, but air without enough oxygen in it and too many things that aren't good for carbon based life.) Luckily, your camera isn't a carbon based life form needing to breath, so it shouldn't particular care.

You will likely want a longer lens though. You are not going to be able to get close to the lava flows for safety reasons. I would recommend a minimum of a 200mm lens and if you can get a 400mm lens or longer, that's probably preferable. 85mm is most likely not going to cut it from a safe distance.

Lens hood doesn't matter for a light source in frame, but it does matter for light sources out of frame (ie, the sun) so use conventional wisdom about the lens hood. I'd generally use one because it isn't going to hurt anything.

The only other advice is make sure to follow the posted notices and be aware of your surroundings. Volcanoes are fun to visit, but they are also dangerous, especially active ones. The actual volcano generally extends far beyond where you see the lava and the rock above it can be very thin. Additionally, noxious fumes that displace oxygen are all over and you won't feel uncomfortable if you go in to an area with insufficient oxygen, you'll feel fine right up until you pass-out and suffocate.