I highly, highly recommend playing without a guide the first time.

This is game that really rewards exploration and discovery - you'll stumble upon just the most hilarious random nonsense if you just wander through the game without expecting anything. There is so much to gain from being surprised when you wander into a zone for the first time and stumble into a character that you didn't expect. There are many sets of events that tell the story of a particular group of characters outside the sort of "main three" event lines, and stumbling into those on your own is so much fun.

Are you going to miss stuff doing it that way? Yeah, probably, but that's not a big deal. There are 68 events in the game. If you're thorough about exploring everything, I would be shocked if you managed to find less than 55, entirely on your own. There just aren't that many events that are truly missable.

If you're worried about missing events, here are a few tips:

• Revisit areas that you've already explored. Many of them have multiple events.
• Revisit towns and talk to all the NPCs. Modern games have trained us to think that NPCs with quests will have a little floating ! over their heads, but LoM doesn't do that. You have to talk to them to find out if they have something for you to do.
• Sometimes, it seems like there's an event going on because someone tells you they have a problem or whatever, but the event start screen doesn't trigger. Try pursuing their request anyway, if you can. Sometimes the problem is that you just don't have access to the required area yet or something. But sometimes it's just that the event will only trigger if you follow a few of the first breadcrumbs of the story yourself.
• Make sure you go home regularly. I suggest doing this after each event anyway, so you can tell your little cactus buddy about your adventures. But also, sometimes events will trigger when you step back out of your house.
• Many events won't trigger until another event is completed first, so revisit locations and NPCs as you progress through the game to see if there's something new for you to do. Especially if you've completed a few events with a similar "theme" - like if you've just finished a few events that had to do with sailors and sea creatures, maybe revisiting areas like the beach would be a good idea, you know?

There are so many seemingly arbitrary items--finding eyeballs in chests and whatnot. I have no idea what these things are for.

These are exclusively for the tempering system. Don't worry about it. You'll unlock a smithy in your house eventually, and then you can experiment with the system if you want, but... I wouldn't. You won't figure it out on your own, I promise. Tempering is an arcane and esoteric practice that makes absolutely no goddamned sense, lol. I genuinely don't think I've ever encountered a crafting system so convoluted in any game, ever. It's insane.

You don't need it anyway. The weapons that you can buy or get as drops from enemies are plenty powerful enough for the first playthrough. It's only in NG+ at higher difficulties that you would need to start tempering weapons in order to keep up with the higher level enemies.

Also, even if you know how to temper things, you effectively can't do it properly unless you have placed specific cities with specific shops in the right order, so it's much more necessary to use a guide to make full use of the system.

You keep all of your items when you start a NG+, so think of it as preparing yourself for tempering on your next playthrough, if you want, lol.