Can anyone give me some advice on the best way to paint polka dots
onto my living room wall?

(Strange request - I know!)

I'm absolutely clueless at any sort of DIY, including painting, so I
want to find the easiest and most effective way of doing this...

My living room walls are a fairly vibrant red, painted a few years ago
with one-coat emulsion. I now want to paint black polka dots onto the
walls (probably dinner-plate sized, or maybe a bit smaller).

I'm guessing the best way is to use a stencil, but then I have the
following questions...

- What's the best way to make the stencil? I'm guessing it's going to
be hard to find a ready-made dinner-plate-sized-polka-dot stencil.

- What's the best way to fix the stencil to the wall without it
slipping? Will masking tape do it? My feeling is that masking tape
won't hold it securely. I've got some gaffer tape, but that will
probably ruin the walls.

- What sort of paint should I use? Will black emulsion do it? (Can you
even get black emulsion?)

- How should I apply the paint? With a brush? If so, what type of
brush? A sponge? A roller? Some sort of spray-device?

- Can I use spray-paint? Is that a good idea?

I'm hoping to get started on this in the next day or so, so any advice
you can quickly give me would be appreciated!

Thanks.