I have limited experience with pedal yaks, but I can tell you that you will not be happy with a 10 ft yak.the only thing they do well is piss off their owners. they wont track straight, and will be harder to paddle over longer distances because of the big flare required to go from the bow to where you sit.
at bare minimum, you should be looking at a 12 to 14ft length. I'm partial to my 10 year old wilderness systems tarpon sit on top fishing yak (paddle, not pedal powered)
if I had to do it over, I'd seriously consider a native watercraft ultimate 145. it's a paddle only, but its stable enough to stand and cast from, has a drop down skeg for longer distance paddling, and can be configured for solo or tandem use. the seats are ultra comfy, and are removable to use as camp chairs. theyve been on the market for a while, so used boats are out there.
the best advice I can give is to attend demo days by local shops where you can sit and go out in a bunch of different models. then you'll know what your back, butt, and wallet can agree on. well, 2 outta 3 of those.