I wouldn't go for coffee lake just yet - not a Ryzen fanboy, but I would either get ryzen now if you're impatient to get started, or wait until Intel releases cheaper MoBo's.
If you are going for coffee lake, I wouldnt get the 1070 ti. Get a 1070 and squeeze as much money from the difference between the 1070/1070 ti on perhaps a 8th gen i7.