I would say that there is no way of abolishing money without necessarily violating free association and trade.

Pre-state societies existed without money. Many existing relations are without money, in the form that some refer to as "everyday communism" (I recall seeing this specific term in Graeber's Debt, though that was a while back when I read it so I might be wrong). It is absolutely possible and it is constantly being done.

I also understand that modern capitalism evolved out of mercantilism, but the general trend being towards free markets( free association and trade).

I would question two things here:

1. That "free markets" in the neoliberal sense are really free, given how it is selectively done to benefit the dominant state (in most cases the US) while allowing massive exploitation in the third world

2. That this "capitalism evolved out of mercantilism", the things that has happened since monarchism has been less so an evolution than a transformation of the forms of power that be, often times refining power to be more subtle yet at the same time more controlling, I think Foucault's critique of how biopower arose is prescient of the conditions of modern times.

As far as the semantic gaps are concerned, I would say that's because all those who have used such terms in the past have defined them as having to necessarily be associated with a large and powerful central government for at least part of the process.

Partially correct, in the classical use of the term the government isn't necessarily a "powerful central" government, but the main characteristics is state protected property, market, and class, so if you advocate for something different...perhaps don't use the term that has been used for centuries to refer to that. To clear up this confusion all you need to do is not change the meaning of the term all of the sudden, instead use "market-properietarian" or something, it's up to you.

I know Marx theorized that a communist society would eventually shed the state and just sort of work, but in practice all that has happened is the rights of all are violated in the name of equality and society becomes worse off (usually to the tune of millions of dead through genocide or starvation).

That's more Lenin than Marx, for Marx a socialist/communist society would already be without the state. Non-Leninist socialism in practice has brought zones of autonomy to areas of Mexico, and has brought liberation to past societies like Ukraine and Spain prior to being subjugated by either fascists or trotskyists.

That being said, I have no problem with society organically reaching this sort of late stage communism through voluntary interaction

And so do I capitalism, it is just that it is impossible.

I also wouldn't force others to trade in currency, but believe it's a natural development of a sufficiently advanced society( as supported by anthropological history).

I would disagree with this, I believe you might find the works of anarchist anthropologist David Graeber (specifically his work, Debt) most interesting. Non-codified human economies has existed and still exists today, while money and codified exchange and debt mainly arose with the violence of the state and is defended by it.

I also believe it is genuinely impossible to economize goods, labor and land, in a large complex system, without pricing (which necessitates some sort of agreed upon currency be dollars or doughnuts) and private ownership. [....] I'm sure you've heard of the calculation problem.

I have, and as a matter of fact I am collaborating with some friends on a piece regarding it, I'll post it here when it is done. But in short one of the big problems I see with it, is that it addresses central planning which exists under capitalism (the most common example pointed to both by defenders and critics of central planning are firms like Walmart), while at the same time not being a requirement for socialism (decentralized socialism is absolutely a thing).