Hey there, doriandiaconu.
Seems like the laptop uses a standard 2.5" SATA drive with 9.5mm height. This means that any standard 2.5" drive should work with this laptop model. If you think that a 250GB SSD will be sufficient in terms of capacity until you get an HDD to replace your optical drive, then I'd recommend that you go for the SSD now and get an HDD caddy for your HDD when you decide to get one.
As for the SATA, definitely go with SATA III.
Hope that helps.
Thank you! In the end I settled down for a 500GB Samsung EVO SSD.