Thanks for your considered response. I will be terse in my reply, but link to references that are those that clarified my thinking. Assuming you are discussing in good faith, I would deem those links essential reading to understand the MMT position properly.

I will not quote your responses but try to reply directly.

1. The MMT position is consistent with the chartelist view that fiat currencies are worth something because the state requires payment of taxation in said currency. It's as simple as that. Enforcing of taxation in the state currency is a sufficient condition to imbue it with value. Note that this is not a necessary condition, but it is sufficient. The historical record suggests strongly this is how money evolved and existed historically, contrary to the oft presented view that it evolved from barter using a commodity intermediary.

There are various texts that discuss this but I'll link to Warren Mosler for an MMT definitive position. He discusses the chartelist position with references in this paper:
http://moslereconomics.com/wp-content/graphs/2009/07/natural...

Moreover, as a simple point of logic, fiat currencies must spend before they can tax. How else can the tax be claimed if the money has not be spent or lent into existence?

2. MMT asserts lending to a government is unnecessary. The balance sheet can just as easily represent cash as a liability as bonds as a liability. The requirement to issue bonds is purely political. This is a factual statement and has been demonstrated in a recent UCL paper for the UK:
https://www.ucl.ac.uk/bartlett/public-purpose/publications/2...

I understand there is a similar paper for the US but I don't have a reference to hand.

Moreover, in Mosler's document above, he argues that the natural rate of interest is zero, making bonds essentially equivalent to reserves (which serve an important role as risk free savings).

3 and 4 I'll discuss together in the context of the job guarantee scheme, since that's the primary automatic stabiliser policy advocated by MMT. The JG sets a pricing anchor, defining the value in currency of a unit of lowest price labour. This is really important - the value of the currency is tied to a specific real resource. I'll be honest that this was the bit I found hardest to grasp, but Warren Mosler has a very elegant justification which made it click (he calls it "employer of last resort" here, but it's the same thing):
http://moslereconomics.com/wp-content/uploads/2019/02/Full-E...

5. As discussed, MMT asserts that there is no need to borrow money. Separately, the bond market appears to be rather more resistant to low interest rates than might be assumed from a mainstream analysis (bond sales with negative real term returns are still oversubscribed). This fits with the understanding that bonds are really just interest bearing reserves, and who wouldn't want to buy something interest bearing when the alternative is no interest (CB reserves).

I'll be honest and say I can't actually contribute more to the discussion until we're talking in terms of those references, and even then I may not be the best person to discuss them. I'm happy to discuss more though if posed in good faith.

The big point about MMT is to have a much better understanding of the system so as to have a better understanding of the available policy space. The main test of MMT would be to implement a JGS and see who turns up.

Edited for clarity.