No
Stain is applied to wood before any sort of sealer
stain enhances the color of wood to bring out grain
different densities of wood absorb the stain at different rates
paint, varnish, lacquer seal out water after a stain is applied.
Lately stain is hard to find the one step idea stain,sealer, clearcoat all in one is the norm the results are so much inferior i have no idea how they can sell that junk.
perhaps that is why you can find so much nice furniture on trash day
Generally, yes, although the water-based stain may run a small amount after application if the wood still has a lot of oil present in it. After 15 years, it should be okay.
yes
You should check the label on the specific product you're planning to use. If the label states it will adhere to wood with an existing coating, then it's fine to use even over an oil-based stain. (This is because once thoroughly dried, oil-based stains behave the same as water-based stains.) Some products, however, will require the existing stain to be stripped from the wood, or to apply a primer coat over the existing finish before applying new stain.
You can but it wont last, you will have a bigger peeling mess.
If you paint over the "weathered" paint, it will chip and cause the stain to come off. Also, the stain needs a clean sanded surface in order for the wood to absorb it. Otherwise, there is no reason to use stain.
yes.
yes
You can wash it off with a moist sponge, but it is likely going to still leave a stain. Drywall is very porous. It is basically paper over chalk. There is just no way to remove some stains. If you want to paint over, but the wood stain keeps bleeding through, cover the stain with a product like Killz. It sometimes takes a couple of coats. Once the Killz is totally dry, the stain should quit bleeding though. It can then be painted over. Just keep in mind, if you are using a water based paint, use water based Killz. If you are using an oil based paint, use an oil based Killz.
Generally, yes, although the water-based stain may run a small amount after application if the wood still has a lot of oil present in it. After 15 years, it should be okay.
can i use water base paint over oil base paint
Yes, you can, That's the normal way.
Yes. Clean and degloss the oil based paint, apply an oil based primer, then apply the water based paint.
yes
You should check the label on the specific product you're planning to use. If the label states it will adhere to wood with an existing coating, then it's fine to use even over an oil-based stain. (This is because once thoroughly dried, oil-based stains behave the same as water-based stains.) Some products, however, will require the existing stain to be stripped from the wood, or to apply a primer coat over the existing finish before applying new stain.
You can but it wont last, you will have a bigger peeling mess.
yes
No, you can't .