Gee, I'm no expert but there's the basics to keep in mind...so just bear with me. I will focus on succulents only because that's all I plant now especially hardy sedums and semps.
First thing I noticed on some of the most interesting, perfect sized containers one might use is no drainage hole. Gotta have that especially for succulents.( Marilyn and Karen, you also know about need for drainage in the soil.)
Also gotta know which plants stay small as they grow. That will take experience and time. You both know that a small plant has potential to grow to be a big plant. For some reason some people think small semps won't grow to be big semps. That's why one needs to know which are the semps and sedums that grow in number/size but stay small. I have heard Sempervivium barbulatum 'Hookerii' mentioned as one of the smallest with the mini one as 1/2" and the small as 1/2"-21/2".
Also most Semp Rollers stay small. Marilyn, remember my "Jovibarba "casserole"?
Those of you who have collections of semps should be able to see which ones have been thru a couple of generations and still stay small. Those are the ones to consider for your small containers. Also if you don't have semps that small, just use a slight "bigger" small container to keep the scale of your desired plantings.
I have found that the Sedum album that I use has a mini one and a small one. Same with S. dashphyllum...a small one and a larger one. These sedums stay small but they grow out and over so that one needs to cut them back to the confines of one's aesthetics and one's container. But they don't need to be pulled out.
Remember that just because the small container has less plants doesn't mean less maintenance. One still has to know what the needs are for what's in the pot regardless what size pot they are in. I find that a small container can give a person satisfaction as much as a large garden can. The entire garden is just in a smaller "yard".
All the above sensibilities apply to any type of plants.
*edited to add database photo of Semp. b. 'Hookerii'
