Question about HP 250 G5

Yes should work (should be 2 ram-slots)
https://www.youtube.com/watch
https://www.youtube.com/watch

an extra hdd/ssd probably only works via adapter
ICY BOX IB-AC642 SSD/HDD Adapter
if you do without the optical drive...

I would also be interested. According to HP Germany, it has RAM slots (i.e. not soldered), but you can't expand the RAM...