First it helps to understand what a black-body is: a perfect black-body is a 'material' that absorbs all radiation that shines onto it and emits 'black-body radiation', which is a broad spectrum of radiation that peaks at a frequency related to the body's temperature. It is important to understand that a black-body isn't necessarily 'black. If the black body is relatively cool, less than a few hundred degrees C, it will emit mostly IR radiation. But a hot black-body (100 C and more) will have the peak in the visible spectrum, and a very hot black-body could have an emission peak in the UV, X-ray, or gamma-ray spectrum. In fact stars are actually pretty close to black-holes in their absorption/emission spectrum. But to answer your questions.
Q1) A box, painted internally with black paint and/or with lots of internal baffles is a pretty good black-hole radiator. If you shine visible light in through the hole (including laser light if you wish) then most of the light will be absorbed in the box and a reasonable approximation to black-body radiation will be emitted through the hole. But in practice, you don't need to shine anything in. The box will emit light in a frequency range related to its interior temperature, so you can keep it warm by sitting it on a stove, blowing hot air on it, or wrapping it in cuddly rabbits.
Q2) The most important qualities of lasers are that they emit light that is coherent, collimated and monochromatic. So, all the waves at the same phase, all moving in the same direction, and all at the same frequency. Black-body radiation is the exact opposite of this: phases all mixed up, light emitted in all directions, and a very broad spectrum. So a black-body isn't and cannot act like a laser.
Q3) All materials emit light. Whether they emit IR or other frequencies depends (mostly) on their temperature. The only benefit of a hole or cavity, is that light that shines in will most likely be absorbed after multiple internal reflections, so won't bounce straight out at the same frequency. So a shallow hole with a reflective interior will not be at all like a black-body.
Q4) Ignoring the question of what an IR black is, if you paint the inside of a hole with a paint that absorbs most/all of the incoming radiation it will probably be a better black-body than a hole that you leave unpainted. But in the real world, paints and other materials also have emission spectra - by which their thermal radiation differs from that of a perfect black-body radiator. So if you chose the wrong paint you could make things worse. Actually, if you had a perfectly absorbing paint (black at all frequencies), then you don't need a hole at all - just paint a spot of it on a wall and that spot becomes very close to a black-body radiator.
