Nikolai Stepanovitch wrote: No money for big irrigation systems or equipment (somehow I doubt most homesteaders use that anyways) and no money for our own excavator to dig irrigation ditches everywhere.
Nikolai ... I'm trying to balance that statement with being on as little as 5 acres. If you're on five acres, your irrigation problems can't be that big! You can get water to 5 acres with very inexpensive drip tape and supporting equipment - presuming you have a water source that can actually handle 60+ gpm.
I don't mean to dismiss your concern - this is an important consideration! If you're planning on commercially farming right away, then you'll either need to match water to your planned crop, or match your crop to the rainfall & water. I like the approach of observing for at least a year, then getting going with earthworks. Water strategies are built into Permaculture and so you might consider hugels, silvopasture and water-stacking techniques and bypass the whole idea of irrigation instead.
And definitely no need to get a loan on a tractor. Tractors are tough and can live (?) a long time. A used one can serve you well!