You can get Kubota OEM pin stabilizers for $150-175 depending on the tractor (mine were $170 for an
L3200).
As for tires, we can debate all over the place. My personal opinion, which only matters for about a 12-16" radius around my body, is that turfs would be best if mowing a lawn was a priority, or if snow removal was a priority. If loader work is a priority on any surface (including lawn) I'd pick the R4 tires, or for general utility work on any surface, I'd pick the R4s. If using ground engaging implements, R4.
I have had both turf and R4 tires, and both will tear up a soft muddy lawn in 4WD or 2WD. Both will be easy on the lawn in 2WD for "straight line" work, like driving across the lawn to move firewood, etc. Where turfs matter on a lawn is if you're constantly doing laps with turns, etc, like in mowing. There, the turfs will definitely be easier on the lawn.
I wouldn't automatically get turfs just because there is a lawn on the property, only if mowing that lawn was one of the priorities. I drive across my lawn on R4s all the time without any damage. If I start doing excessive work that requires a lot of turns or going into soft areas, then it will start to be an issue. The turf tires on my other tractor are definitely easier on the grass in those circumstances, but even they will leave ruts in soft areas and tear up the turf if I make a lot of turns.