Ask the seller if that's a DUAL X5690 or single X5690. If dual X5690, $700(Euro) is acceptable (still not cheap, but by considering it's not that straight forward to self upgrade a dual processor 2009 Mac Pro, I will say that's acceptable).
16GB RAM isn't much, but sure good enough for basic Photoshop and FCPX.
5770 is very weak now, but if you only do simply FCPX editing, may be it's good enough.
In any case, it's very easy to upgrade the RAM and GPU. Install a Sapphire PULSE RX580 and then upgrade to Mojave should able to make the system more responsive, and give you must faster rendering time in FCPX.
16GB RAM isn't much, but sure good enough for basic Photoshop and FCPX.
5770 is very weak now, but if you only do simply FCPX editing, may be it's good enough.
In any case, it's very easy to upgrade the RAM and GPU. Install a Sapphire PULSE RX580 and then upgrade to Mojave should able to make the system more responsive, and give you must faster rendering time in FCPX.