By growing some plants in containers/pots you have the advantage of being able to move them around in leaf and see approximately what they'll look like when planted in the ground. I say approximately since you cannot account for growing to mature sizes eventually but you'll get a colour and texture/shape picture. While growing plants in pots for a year will give you a growth advantage over buying those plants smaller next year, most of the first year in the ground the plants will need to re-establish their root system to their new soil structure. If you want to give the container planted plants a good head start for their final location next year make sure you use a well-draining, well-aerated potting mix, something heavy in bark fines for example will give you nice, thick roots that'll be closer to what you get when growing them in soil rather than most commercially available peat or coir based mixes which really are intended only for growing annuals and will end up forcing the plants into growing thin. thread-like roots that'll be unsuitable for growing in regular soil and set the plants back for top growth quite a bit next year.

I grow most of my hostas in pots and have found best success with a 5-1-1 mix consisting of 5 parts bark fines, 1 part peat or coir and 1 part perlite with some CRF (controlled release fertilizer). You may have to shop around to find the bark fines. In my neck of the woods -Richmond B.C.- I end up having to drive to Lowes in Bellingham WA to find a hardwood bark mulch with small enough chips to serve as base for the mix, you want chips/fines not much larger than a dime.

Good luck with your adventure!

Pieter

BTW, you really posted this in the wrong forum......

Thank you so much for the great advice! Wrong forum eh? Time to educate myself!