In the frame of the R&D activity foreseen for the first phase of the SPARX project, the SPARXINO test facility is meant to provide an ultra-high electron beam at 1.2-1.5 GeV, able to drive SASE and seeded FEL experiments in the 10-3 nm range. The proposed layout is analyzed regarding its sensitivity to laser pulse jitter effects and microbunching instability limitations. First simulation results are presented.