Someone please correct me if I’m wrong... being a loach, I think they are social but not necessarily schooling. I’ve found that with buddies they are more relaxed and less skittish. I have 3 dojos in one of my 135g tanks. I think a 55g would be good, a 40 might be ok as the only bottom dwellers. Just keep in mind they are like colder temps, I’d say no higher than 75f.
Mine are maybe a little over s year old and are about 6-7”. I forget who, but I know at least one other person on this forum has some also and are older than mine so might have more/better advice. They are so cute and very peaceful.