Is it fine to follow a completed build with no guide?

In my experience, yes, if you know how the build works, what are the damage sources, the defence layers, etc. Better to have several examples of the same build, which can be easily find on poe.ninja

If you dont know the specifics of the build, you may have some issues with it, like when there are versions of the build depending on a specific unique. If you don't have it, the passive tree is different, the gearing might be different, etc.

I do this with most builds, scan for key keystones and follow paths based on what i need at the time rather than a specific order. But I also play SC and gauge dying a lot as a time to re asses my skill tree so maybe not a good example

Yes, but it's definitely harder if you are new to the game.

Most players can get through the campaign just playing blind, but after that point it would be a good idea to look up guides/YouTube videos about the game and find a good build that would be easy to respec to as you go through low-tier maps.

For HC idk lol

Absolutely. You just need to known which passives to prioritize early on and when to swap to weapon set passives and which defenses to take first, etc. Once you do a couple builds it becomes much easier. Also, not all skills are available early on, so that's why you have to make some choices before the build fully matures.

This looks very similar to a build I played. I followed Phazeplays disciple of Varashta Djinn build. Find that on YouTube and you've got a path to follow.

One of the easiest builds i found for levelling

I almost always make my own build until I get to T-15, then i go meta because my build is slow as fuck.

I’m new too, at level 83 now. However from my previous experience with Diablo, I just don’t have fun with games like this following a guide. Although tedious, I like the thrill of discovering some crazy new shit for my homegrown builds that make me noticeably stronger. Following a guide just takes all the fun out of it for me.

There are certain things I look up, but it’s more game mechanics and not 100% build related. (Mostly the bonkers complicated crafting the game explains in zero ways)

Of course it's fine, it's your playtime. I have way more fun not following any build, guide or tutorial though. What makes PoE2 special is the incredible builds you can make, and at least 90% of the fun for me is creating my own builds.

It's fine if you already understand how stuff works and what synergies are in play. Then you don't need a guide, you only need a build. But if you're new to the game then you might get lost or miss some crucial part of the build that makes it work without proper guide that explains some basics.

That being said, poe.ninja is pretty good source of ideas when you're trying to tweak your build and not exactly sure how to approach it.

As long as you understand the majority of the build, probably. POE2 is not that complicated in build diversity at the moment, wait for a few more seasons and uniques and you'll have a much harder time following builds blind.