E5-575-320P- what kind of SSD to upgrade

Hi again, i own a Acer Aspire E5-575-320P, better known as: NX.GE6EH.014

In a previous topic i was shown there is a special connection for M2 ssd.
But i am not sure what kind of PCI Express i need for this.
2nd i am struggling if i should buy a M2 or a 2.5" SSD since the last are much cheaper.
3rd could i place a 2.5" SSD in the empty DVD bay (there is no DVD player in this model)Is there a connection on the mobo there that is SATA 3 - 600MB/s as well?


Help is very welcome.