Yes you can, just clean the old stain with steel wool or fine sandpaper before you do.
If it is flat paint, you can apply the texture without any additional preparation. If it is a gloss or semigloss, you will need to rough up the surface with sandpaper first.
Yes, that would work as a painting technique.
If the door has a primer or a paint on it then no. Stain needs open grain to work. Stain seeps into the pores of the wood. If there is a coating, i.e. the primer or paint, then the stain will have nowhere to go. It will just sit on top of the coating until it is wiped off or dries in ugly blotches.
As long as acrylic is solid and not flaky you can.
If it is just the stain with no top coat or sealer on it, just wipe it down with a rag and mineral spirits, paint thinner, Lacquer thinner, anything to put the stain back into solution.
yes you can and the stain can change colors if there is a juice stain for example thats red and a grass stain the stain color could change
Yes, but only if the stain is a few years old and really dry. You have to wash the stain thoroughly to remove the chalked pigments and then prime it to seal the checks in the wood. One disadvantage of stain is that it will not keep the wood from checking as it dries. Either a latex of alkyd primer will work well. You can then paint it with your latex top coat.
yes its a porous surface and will absorb liquid and stain
it depends on how deep the stain is.the top layer of skin on you is realy dead skin.
Use whatever sealer is recommended for the paint or stain that your going to use to finish with. Just be sure to seal the baseboard on all surfaces, front, back, top and bottom
Yes
Most paint grade mill-work (mouldings, widow frames and doors) are not designed to be stained. They are created of many small pieces of woods, joined by something called a finger-joint. The wood-grains of the pieces, are not necessarily pretty to look at. For the best looking finish, it is best to prime and top coat paint grade mill-work. If you really want wooden mill-work, spend the extra and get good stain-grade mill-work.