you can connect all 3 screens and it should work.
if you're only gaming on one of the screens the GTX1070 will have no issues to keep up as only the resolution of the single screen is really relevant
if it's a 1080p screen - have fun and knock yourself out
if it's a 1440p screen you might wanna upgrade to a 2070S or better depending on the games you're playing
you can connect all 3 screens and it should work.
if you're only gaming on one of the screens the GTX1070 will have no issues to keep up as only the resolution of the single screen is really relevant
if it's a 1080p screen - have fun and knock yourself out
if it's a 1440p screen you might wanna upgrade to a 2070S or better depending on the games you're playing