I have a similar build and I had a 600w and it was not enough.
340w is in ideal condition you want to get a PSU that is double that at least.
You need at least a 750w PSU for this build otherwise if you try to even overclock or if you want to upgrade the GPU or add another one you will need to buy a new one.
Even if you don’t want to overclock you better leave room for future changes.
And I agree get a secondary HDD storage.
And if you go for a 980ti definitely get at least a 750w PSU but a 970 is a powerful card (I have the same one).
You can wait for Skylake and get a DDR4 motherboard.
And get windows 10 I am using it since the start of the preview and its a very good OS better then 7.