One thing I'd like advice on is how do you know how much chain to fit. I ordered 3 for my Challenge Furai recumbent and I've no idea how you measure off to get the correct length. The links you get to join up the chain apparently are fit and forget. They cannot be reopened so I don't really want to be messing about with a chain riveter which may affect the performance of the chain.
No idea about this 12 speed stuff, but the rule of thumb is "enough that the drivetrain works properly in big:big plus a bit if you anticipate extending the boom at all". Presumably with 1x you don't have to worry about running out of derailleur capacity and the return-side chain going slack (which is relatively undramatic on recumbents, and greatly preferable to things jamming up).
I'm in the habit of keeping some clean worn-out chain around for these sorts of experiments. It doesn't matter if you weaken a chain by splitting and re-joining links if it's only going to be fitted for 5 minutes to determine the correct length. Otherwise, I'd suggest bodging the chain together midway with a cable-tie or something - it won't be able to run, but you should get an idea of what the spring tension will be like in the given sprocket. Not sure how you'd work it out theoretically, given that it's as much about leg length as it is about drivetrain components; you'd need accurate measurements of everything. Obviously if in doubt it's better to err on the side of longer.
ETA: Crosspost with Brucey
