You are mixing up a number of terms here. Is venetian plaster a 'paint' or a 'plaster' to you? It is typically marketed today as a paint, heavily thickened with fillers, but called a plaster.

So will paint stick to paint? Yes, no, sometimes

Will plaster stick to plaster? Usually, sometimes no

Will plaster stick to paint - almost never

Will paint stick to plaster - usually, unless it is fresh lime.

Cracking is common in paint, because the fillers are so fine (usually calcium carbonate and mica). Cracking is also caused in plaster by fillers too fine, placed too thick, or too much water

Lime putty is simply a chemical called calcium hydroxide. The issue is if there are 'contaminants'. Very rarely, in lime mean't for fertilising cattle fields, there is a higher level of magnesium (cattle need magnesium) and this will cause a problem for outdoor fresco, in the frost, maybe. The guy that was so against 'magnesium' in lime was also the 'expert' who threw all his sand away because a raccoon had walked across it in the night.

I am one the ones who considers 'Venetian' Plaster to be a plaster - it is the final coat (not including beeswax) of a three (or four) coat lime plaster process using darbies, plumb bobs, and a polishing trowel. The final product is as smooth as a piece of glass and is called a "level 5" or "level 6" finish by architects and designers. It is rarely seen today outside of resorts, casinos, etc. It is an expensive wall mean't to last two hundred years, and is often mistaken for a sheet of marble or stone. A true lime plaster wall should not be painted for one year (recarbonation, etc.) so this caused all sorts of grief in out hurryup culture - by coloring the plaster with variations, and then sealing with beeswax (still allows to breathe) you have a wall which is attractive and resists household stains, etc. It has to be done properly because it is glossy or semi gloss - it will show every dip and wave around - at the worst time - the finishing steps. The gloss also gives the depth and illusion of stone.

So you have to decide do you want to learn how to plaster, or do you want to learn to to make paint sort of look like plaster. Usually it is the customer who gets to decide - but in Canada and the US, there are so few true plasterworks to inspire, and too much industry marketing emphasising the now and immediate.

Mason's of all types used to consider a 100 year life span as the goal - now I constantly see construction products with a "lifetime' warranty - 25 years.