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For a supine recumbent, FWD can reduce weight and driveline flex. Twisting the chain to steer is fine except for parking type maneuvers. It is better to add idlers than to let the pedals move with the steering or put the pedals above the wheel, unlesss the wheel is exposed below the main body. Internally geared hubs have more friction than derailleur setups except in direct drive, and in a top speed run, most of the time you are accelerating. It is tempting to use an intermediate block and two chains, with two or three derailleurs, but this costs maybe 3% more power than idlers. Idlers can float sideways as the chain shifts. Clearance is tight - try using the narrowest chain, but not many ratios, with a triple crank. Use an extra-big chainring, and try to stay away from tiny cogs - efficiency drops off quickly under 15 teeth. ( With a small wheel, it may be more tempting to use compound gearing.) An oil-bath chaincase might be worthwhile, too.
Wheel sizes probably should not vary any more than they did on the penny farthings, which were also done small-in-front. That should give you some wiggle room.
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