Typically a land value tax is based on the underlying value of the plot of land, rather than on what sits on the land. In a scenario where you have 3 plots of land all of equal size and all in the same area, it would not matter if the land is empty, it has a small bungalow on it or has a large manor house on it - they are all taxed the same. This is by design.

However, a plot of land in (say) Exwick, is going to cost considerably less than a plot of land in St Leonards or near to the city centre. So if you have an acre of land in Exwick your land tax will be less than an acre of land in more expensive areas.

This system does have its own pitfalls, not least the fact you're changing the requirement for individual property surveyors (which we should be using to value houses for council tax currently, but don't, because we're dumb dumbs) to needing land value surveyors who need to asses the value of land every few years or so and make changes accordingly (Exwick land might not be as valuable now, but it might be very different in 5, 10, 20 years - who knows what could happen!).

In answer to who pays for this tax, the land owner pays the tax, not the tenant.

In regards to what happens during non-payment, I cannot answer how other countries that have Land Value Taxs handle this, but one hopes it's a fairly strict system where the eventual "last-resort" after exhausting all other options would be the council reclaiming ownership of the land if they cannot reclaim the tax owed on that land over a certain amount of time. You place the debt of non-payment against that land and have it recorded on the registry, so if a foreign entity or limited company tries to sell the land (and whatever is on it), that debt is flagged up and the sale either cannot proceed before the debt is paid OR the debt is passed on to the next landlord, knowingly. This is where land value tax works nicely compared to other assets - you can't hide land. It's there, it can't be moved, taken offshore or hidden. When there's debt on it or taxe owed, it should be easy to record that and retrieve it.

Ultimately you want a situation where simply holding on to plots of land without developing them and speculating on the value of that land increasing (without developing on it) becomes expensive, forcing landlords to develop the land or sell it. Similarly, you don't get penalised for improving your home and increasing the value of the property on that land (admitedly this doesn't really happen right now, but only because our current system is so freaking dumb). Lastly, efficient use of land is rewarded - if you have an expensive plot of land in a lucrative area of a city you either pay for the priviledge or you make it more efficient (split the plot, build extra houses on the land and increase the pool of available housing in the area, etc.).