I used to keep mine in a standard 40 gallon drilled aquarium and they bred like crazy. I would say if you can find any keep as 1.1. I eventually gave them to Pat Nabors as the male called constantly and it was just about the loudest call of any dart I had ever heard (when I was on the phone people would always ask what kind of bird I had). The calling was so annoying I got rid of them. The male protected and watered the eggs as well as any dart parent I have worked with. The tads seemed very hardy but once they broke their front legs they would drown in almost no water, I started pulling them with half their tails. In the end I could not give babies away and I believe Pat had the same experience, eventually the pair died.
Bassleri should be handled like other large Epipe frogs including silverstonei and trivittatus. These species are usually hard to get breeding but once they start they become very prolific or at least very consistent. Large frogs need large vivs, epipes are leaf litter frogs, so large squat vivs is the best choice. see Mark's post above, 40 gallon tank, that's what we're talking about.
Leaf litter, slabs of cork bark, driftwood and some densely planted areas will all contribute to the frogs feeling secure in their enclosure. All 3 of these species are shy frogs and need places to dive into for cover and hide from each other. Like other Epipes there will be a pecking order where the stronger larger frogs bully the others, so be watchful, especially with smaller males, they may need to be pulled. Again as Mark suggested keep them in pairs for best results.
Another important ingredient to breeding these frogs, as with all Epipes is water. Large water features like pools or running stream of water should increase the likelihood that the frogs will reproduce. Anyone who has idle pairs without a large water source should consider new quarters for the frogs.
BAssleri is one of the Epipes that can change color intensity with mood and social place. I've seen this with younger males that have reduced coloration and almost appear to be females. The boldest alpha male will almost always be the brightest colored frog in the group.