(1) and (4) yield that all light, including light spells, pass through. Heat is infrared light. Thus while the wall stops fireballs, it provides no protection from the heat from a tide of lava and such.
No. Just No.
By your logic, a thermos wouldn't work. Given that they're still selling, your logic is flawed.
Heat is transmitted through three ways:
1) Conduction - IE: things touching each other. This is the major way that heat is transferred
2) Convection - IE: things touching air that's been heated up by something else. That's the second most prevalent manner of heat transfer
3) Radiation - Things get so hot they start glowing, emit photons, and send heat to something else. In general this is the least effective manner of heat transport - although with something very hot (for example, the sun) it can still have an effect.
A wall of force completely cuts out conduction and convection, just as a vacuum would. Radiation goes on through. Although you'd no doubt feel some warmth due to the magma's thermal radiation, it would certainly be below the threshold of causing damage.
I believe precedent puts Walls of Force at 1 inch thickness. I can't remember where I've seen it off the top of my head - Stronghold builder's guide?