Read the instructions on that particular composite and it will explain what it can be painted with. -I don't know because you haven't mentioned the name of the product.
Did some trim work and got some stain on my composite decking how can I remove it
To remove decking paint from a caravan, start by testing a small, inconspicuous area with a paint stripper or remover suitable for the surface material. Apply the product according to the manufacturer's instructions, allowing it to penetrate the paint for the recommended time. Use a plastic scraper or a soft brush to gently lift the paint, then wash the area with soap and water to remove any residue. Always ensure proper ventilation and wear protective gear during the process.
There is NO type of paint OR stain that will work effectively on vinyl decking. If you want a quality job it's necessary to take off the vinyl and re-surface the wood before staining it.
Yes, use a good primer first. I do it often.
No fence paint does not have as much wax in it and it wont last very long before you have to paint it again. As decking has a lot of foot traffic as obviously a fence does not. Take it from me I found out the hard way. Yes deck paint is more expensive but will last a long time.