i guess it all depends on what you want to fish for.
I've got a Extreme Bandit which is pretty similar to the pic of the one you have up there,
I'm not a big fella (under 6ft and 80kg) and i've had a shoulder reconstruction too, and i find i can quite easily lift my yak on and off my Barina.
I've hit up more exposed waters before on it - i've fished from scarborough all the way down to woody point, as well as the surf side on bribie, and i found while the yak was fine if there isnt too much wind or excess chop around,
the second the wind and chop starts getting up they can become rather uncomfortable and while i'm pretty confident in the water, it can become pretty dangerous out there in bad conditions on a small yak.
So if you plan on just fishing creeks, up the passage and around places like redcliffe on those rare perfect days a smaller yak will do the job,
however if you want to head offshore and fish open water i'd get something a bit longer and stable.