UEFI replaces BIOS
https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface
Legacy is just a boot mode that ensures backwards compatibility.
So it wont change anything else.
I would choose this mobo:
http://www.kilobaitas.lt/Pagrindines_plokstes/Asus/ASUS_H81M-K_Socket1150_Intel_H/90MB0HI0-M0EAY0/CatalogStoreDetail.aspx?CatID=PL_660&ID=573078
Unless you need more features...
The CPU will bottleneck the GTX 970 and I don't think that PSU is enough.
Maybe get this:
http://pcpartpicker.com/part/intel-cpu-bx80646i54460
+ a H81 mobo and this:
http://pcpartpicker.com/part/corsair-power-supply-cx600