It’s late so this came out a little stream-of-conscious-y, apologies in advance… In my defense I was just reading some of Lion Kimbro’s 2003 book How to Make a Complete Map of Every Thought You Think which introduced the idea of MOCs and it is absolutely roughly 100 pages of stream of consciousness blowout, so it affected me a bit I think. 
I’ll bite. Having used multiple note taking systems in the past I’ve coe to Obsidian along with a Zettelkasten-style approach at the same time. It’s given me a chance to radically rethink how I take notes, or rather to rethink how to develop a system that works around the way I want and need to take notes.
The fact is I’m a metadata minimalist in many ways. I barely use tags and the ones I do use are essentially only for note types, and of those there’s really only two that actually have any meaning: source-summary-in-progress for notes containing all my highlights/notes from a source, and source-summary-complete denoting that I’m done processing that source.
That’s really it as far as tags. (I technically have a couple others floating around from early on in my thrashing figuring out how to set this up, but they are pretty much meaningless)
And even with those they aren’t actually needed. What I found is that instead I have a different way of adding “metadata” to denote sources: I put them all in a sources folder, and I adopted a syntax I saw Nick Milo (I think) use where he prepends the title with S-source name.md. So now they are easily distinguished in links and in the file system. And I could even get rid of the -complete tag because when I’m finished processing a source I could just drag it into a completed folder.
Another piece of metadata that I apply without thinking is the date, because I use Zettelkasten IDs in (most of) my notes. (most = not sources, and a few other notes, but most use it) The reason I do this is to eliminate folders and just dump all my notes into a single folder, so I can avoid namespace collisions. Then I create MOCs when the need arises to create topic entry points into my notes.
For reference I’m a bit further than you, around 500 notes, and I have 7 MOCs. How do I know? Because I just searched for file:(MOC) and counted them. They are in various stages of disarray – the more I use them the more attention I pay to their layout/etc. I also have a “Home Note” that links to the MOCs along with having what are essentially several “proto-MOCs” directly in the home note – proto-MOC is just a fancy term for a bullet list with a heading and some sub-bullets that each link to a specific note somewhere, because I added the note and it wasn’t associated with anything else so I slapped a link to it in the home note and then started aggregating them into groups as that made sense. At some point as a group grows I will spin it out into its own MOC.
My whole focus is to do something very different from what I did in previous note taking systems and tools like Evernote and even wikis, where instead of focusing on the hierarchy and metadata I’m focusing on the process and using a few basic heuristics to guide me. For example, every note must be linked from somewhere not just link to somewhere. My focus is on fluidity wherever possible. I’m even extending this into work project tracking now and its pretty seamless.
The result for me so far is that Obsidian is starting to reflect the way I think and work, rather than me adapting to a rigid tool. And unlike tools like Evernote which expect you to come up with incredibly complex tagging schemes, here every time I try to add a tag and start using it then I fairly quickly get a physical eww feeling and back out of it.
Its absolutely arguable that I’ve shifted metadata into a different form i.e. the S- prefix for sources instead of a #source tag etc, which is true, but at least this way the metadata is visible in the filesystem at a glance as well, which provides some value to me if and when I need to depart Obsidian for something better later on.
One thing I do use in the front matter as a result of the Zettelkasten prefix is the aliases field. I’ve set the Note Refactor plugin to automatically create it for me when the note is created – I use the Note Refactor plugin heavily because it not only lets me auto-fill that field (the ZK plugin does not) but it also forces me to start my thought on another note and then refactor which creates the forward link my rule of thumb requires. Once the Note Refactor plugin creates the note I just quickly remove the ZK prefix from the alias field and then I can update the from note to use the alias in the link if I want, or if I’m not bothered I can just skip updating the from note entirely and maybe I’ll update it next time I happen across it.
I’m also considering using emojis in filenames to denote states for a select few notes like goals, based on an article I came across the other day. Not sure about that just yet but its an interesting idea, if used sparingly. I experimented with using emojis in tags as some like Bryan Jenks (I think) do but every time I quickly abandon it. I’ve also tried using emojis to denote note type in file name but also quickly abandon it. My reason is that I don’t make clean distinctions between “this is a seedling” vs “this is an evergreen note” – A NOTE IS A NOTE, some are long, some are short, some become hubs that build topic clusters around them and perhaps eventually become or lead to the creation of a MOC. But that’s an organic evolution rather than a top down decision. It also eliminates me from having to think “what type of note is this” – right now my note types are simple, its either a source, a MOC, or a permanent note, there’s no spectrum of permanent notes or states of permanent notes. I can’t be bothered with it. I am in the process of adding meeting notes into the mix but those really are just permanent notes because they are a record of discussions and decisions, and are tied by links to teams (and from team notes), and are spun out of a daily note where I take the meeting note and then use the note refactor plugin to create them.
BOTTOM LINE:
- virtually no tags
- “metadata” in filename, sparingly
- constant fiddling and tweaking and messiness
- Obsidian helps me bring order to the chaos so this weird thing I’m building feels right
EDIT I should add my reasons for avoiding tags are that my prior experience with tools that encouraged their use was that they break down horrendously over time. Tags are very weak association tools, just saying “this is of this type of topic” isn’t very helpful. I don’t even use backlinks very much in the traditional sense.
in note names to denote an unanswered question notes and 
for answered question while also getting around the punctuation restrictions in file names. Metadata in the naming convention would also remove the the friction of going into a note and adding a template straight away.
But I hadn’t thought about using two different colors like that, what a great idea. I haven’t settled into a full naming convention that uses emoji but it seems like an interesting direction.
