It depends on what you want to get out of the ssd, if you want a fair balance of speed and storage then you want to get yourself an 2.5" while m.2 sacrifices storage for even more speed and size. seeing as the ssd you get is listed as the only one, I would personally recommend splitting the build into either two ssds or even ssd and a hybrid drive combo (Unless anything other than m.2 is a no go zone). This is due to the fact that modern ssds due to the way they work slow down along the process of writing data.
The following parts list provided gives you an m.2 240 gb ssd to put quick access files such as your O.S. this gives you about 180 gb to work with (recommended not to fill ssds u pall the way) plus a 2 tb sshd to give you a large storage solution. You may already know this and just want speed, in that case your build is absolutely fine.
Alternative parts list: https://ca.pcpartpicker.com/list/NfRw29