Isn't land already taxed?This very much depends on your jurisdiction - the UK has local government taxation which is very roughly based on house size or commercial building use, and is capped so everything above a large family house ends up paying the same rate.
I'd be quite happy swapping the transaction tax and council tax for an ongoing property value tax, but I also know that wouldn't be very popular in the UK which is so dependent on house price inflation.
How do you tax companies which rent their office/production space?
You don't, you tax the rentier. Whether the property is let or not.
Isn't taxing land punishing companies planning for growth? It is not uncommon to buy/rent spaces which you don't need now but you know will be needed in the future?
The process of "land banking" by e.g. Tesco is controversial in itself, since it potentially results in land and buildings left idle or even rotting while everyone waits for the expansion. It obstructs the use of land by others who want to put it to immediate use.
How do you deal with real estate investors?
Real estate investment is usually heavily geared and pro-cyclical, so I'm quite happy to stick them with a tax bill. Especially if it might prevent another 2008 boom/bust cycle.
It's a form of social engineering, like everything else in the tax code, and requires a bit of attention to detail. How to avoid ruining family farmers while discouraging people from reserving vast areas for sporting estates, for example? What of property-rich but cashflow-poor pensioners (the most common objection)?