Perfect Strokes

If its ready mixed yes. the fibrelining paper is 'paste the wall' so you can use any ready mixed paste will be ok. don't use the mix it yourself wallpaper paste as this is made for 'paste the paper' wallcoverings.

You do have to remove tape before the paint dries otherwise you will almost certainly pull off some paint on the wall. once you have got your line established after the first coat it is alot easier to follow the line for the second coat by hand...or at least get as close to it as it needs to be :)

With most satin or eggshell paints you can cover about 10-12sqm per litre of paint.

1 side of an average door is about 1.7sqm
so if painting both sides of door it's 3.4sqm

4 doors, both sides means you have an area of 13.6sqm of door to paint.

you will usually require 2 coats of paint to cover properly so that makes 27.2sqm you will need to cover.

a 2.5litre can of paint that covers 10 to 12sqm per litre will cover 25 to 30sqm so that should be the right amount for 4 doors :)

You'll need to scrape off all the loose paint first, you'll probably find that more is loose than it appears. once all the loose paint is off, you can either sand the edges of any remaining paint to smooth them to the level of the wood and create a seamless transition from the remaining paint to the area of removed paint. or if you have bits of remaining paint in random areas you can apply a very thin layer of wood filler to bring everything to the same level. then you should give the existing paint that remains a light sanding to 'key' the surface. apply a layer of primer to the whole surface followed by two top coats and you're done :)

You will need to remove the old layers of gloss before repainting otherwise you are correct in saying you will see the ridges where old paint surfaces are higher then the areas that were bare.

i would use a paint stripper to get the worst off first. they are good for removing one or two layers at a time. depending how many coats have been put on over time you could repeat this a few times.

once most of it is off, then sand to remove any stubborn paint and to get the whole surface even. (if you can feel bumps, dips etc when you have sanded it, then you will see them once painted).

apply 1 coat of primer then two top coats and your skirting will look as good as new :)