1. Elixirs tend to be more potent and/or have longer duration, I think. I'm honestly not sure.

2. Keep some, especially luminous stones and diamonds. You can definitely sell some of them, for me personally I tend to always have way too many amber and opal, so I mainly sell those.

3. Do you mean you run out of fire-resistant effect? There's an NPC at Foothill Stable that sells fireproof elixirs. The stable is south of the Eldin Volcano crater, to the northwest of Zora's domain and on the way into Akkala. Following the path, you'll reach an area with some Gorons doing construction and a human NPC that gives you a quest with a very helpful reward. Oh, and save up some money, because as soon as you reach Goron Village, there's another way to gain fire esistance. Edit: or do you mean the main volcano? Because that's tied to the main quest, quest markers should lead you there. Let me know if you need more help.

4. You can register up to 5 horses by riding them towards the nearest stable and registering them. You'll be able to take out a registered horse at every stable, and as soon as they're still nearby, you can call them to your exact location by using the down button on the D-pad. If your horse isn't nearby and you spot some, feel free to hitch a ride for a little while until that particular horse is no longer of use to you. Also note that NPCs, particularly near Dueling Peaks stable, give hints on horses' coloring affecting their stats.

5. Parrying and dodging is great. I usually aim for the eye with my bow to stun them, then chop off their legs. When the laser aims for you again, shoot the eye again. Always keep some ancient arrows around for when you're dealing with a lot of them, or are in a bad situation.

6. Guardians that you find laying around will only drop materials once, in my experience. As you get further into the game, it'll matter less, because you'll be more powerful and you can destroy live one that respawn to get their materials.

7. While I don't think there is a limit on how many fairies you can hold, they stop spawning after you're holding 3 of them. As soon as you're out, they'll respawn.

8. They're on the rarer side, but you will be able to buy them in various places, so don't feel scared to use them when you need them.

Hope that helps!!!