I've got one planted in a pot and another in open soil. Both are dwrf varieties - is yours?
My potted one is green leaved and likes dappled shade.
I potted it up in 100% ericaceous, though acer growers have since told me that most acers will tolerate neutral soil too. Since I didn't know what pH my soil was, I played it safe and went for ericaceous.
Mine was in a 3L pot and I planted it 2 years ago into a round pot of about 40cm diameter.
Acer grower lady I chatted to at a flower show advised me to lift it after 3 years, unfurl roots and cut them a bit shorter, then put back into same pot. Then pot onto its final pot after 5 years.
I added lots of grit and some broken crocks to the bottom of mine for good drainage - they like it moist, especially around the roots (no drying out), but free draining too.
I also put some bark chips over the surface to help with keeping moisture in.
I have mine in a sheltered bit of the garden alongside a shed - they do like protection from a very blustery site and the green ones like mine like dappled shade as they can become scorched in full sun. My purple leaved palmatum likes it sunny (leaf colour better) but it dried out too much west facing, so re-sited it to a more sheltered position and it doesn't dry out now.
Hope this helps.