hi, i have 4 internal sapele doors ( dark brown stain colour)..they are all different sizes..wes going to replace but find that the sizes i want do not exist ( in cheap hollow doors & cannot be cut down easily ), so i have decided the paint them..i would like to paint them in eggshell....so to get a really good smooth finish...what exactly would i need to use & do?...undercoat..primer ..sanding down etc.? any or none of those? any advice/help would be greatly appreciated...many thank in advance