We already discussed this one and it's by far not as bad as you think.
It's true every size needs a different approach. I wouldn't say one takes more time than the next.
How about using 4 sheets acrylic for a bigger painting? If you use paper there's no need to use the easel. Jyst place it on the rable (a piece of tape in the middle if each sheet to keep them at their place.
The acrylic or watercolour sheets will work it's what I also use. That cardboard sucks it falls apart. Nevertheless, make every stroke vount. Look begore you start.
By the way, I did gloss/varnish my paper and some have very thick layers of acrylic (not needed? . It feels in the end not different from canvas.
I never made paintings bigger than A4 or A3 except those on walls and that's a different way of working.
Layers can make a painting more realustic but thebquestion is if it's needed and what your style is. There's no need to be the next vooy-cat.
Did you try water colour? White is rarely used since the white comes from the white paper. You could give a light wash here and there which comes from the water you clean your brush with.
Right now I struggke with a canvas with parts paint reguses to stick. I scraped most of the paint off.
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You're right about several things, although, on this card, if acrylic without water ruins it, I imagine watercolor wouldn't even let me get started.