Was arable land easy to come by for a poor Roman or would you be more likely to have a landlord requiring some cut?

In general no, it wasn't easy for poor folks to get their own farm land, and it became harder as time went on.

A plot of land was a common millitary pension; soldiers would retire there and work the land after putting in enough service time. This worked well while there was plenty of decent land in Italy, but became a worse deal over time. Once the prime land was taken up soldiers had to settle for plots of varying quality far from their homeland, which was much less pleasant as you'd expect.

The poorest would likely “sign on” to an existing farm as a farmhand - the story of the Prodigal Son implies that concept was known in antiquity.

The problem was the big farms relied virtually exclusively on slave labor for labor. There were numerous attempted reforms to require landowners to hire free citizens, but I don't recall about any systemic change being achieved before the fall.

> soldiers had to settle for plots of varying quality far from their homeland

So .. Mesopotamian soldiers might have to settle for land in Italy after serving at Arbeia [1], the Roman fort in England rather than return to their homeland?

Or are you perhaps thinking that the Roman Army was mostly made up of soldiers from provinces of what is now modern day Italy?

[1] https://en.wikipedia.org/wiki/Arbeia

Things changed after the transition from Republic to an Empire. One of the factors in that transition was the shortage of land to provide to soldiers, who at that time were mostly Roman citizens.

Not at all. It was so hard to get land that “land reform” was a constant political point.