Don't know how you measure land in Australia but a 1/2 ac. in US that is about 100X200 foot. Just a nice work out on a hill with a push mower. Seeing you can still walk fairly good a self propelled would work for you also.
Sounds about right size-wise. The problem is with my foot and that I can't push against it very well (the big toe doesn't bend anymore) so I end up either hurting the foot or compensating by changing my foot placement which ends up inflaming other parts of my leg. Trust me I'm fit enough (I road cycle 50-100km several times a week plus swim a couple of kms so no issues there) but it's just the actual movement required in pushing a mower up-hills that's the issue.