Hashrate + Power calculation:
1x EVGA GTX 1070 SC: ~450sol/s ------ 140W
2x Zotac GTX 1070 Ti Mini: ~510sol/s -- 165W*2
2x EVGA GTX 1080 Ti SC2: ~740sol/s -- 235W*2
(Yes, you should buy 1 more 1070 Ti if you still have budget).
Total hashrate: 2950 sol/s. With this hashrate, you may get ~1.45 ZEC/month which is about 480$/month.
Power cost: (940W * 24*30)*0.12$ = ~82$/month
So basically you have the return around 400$ if I'm correct.
Your case is mostly the same as me, most of my hashrate is used to mine ETH & XMR, but I just want to test for fun or for whatever, I build more 3 Nvidia rigs to mine several altcoins: FTC, XZC, BTG, ZEN, ZEC, VTC.
You can check the hashrate of zotac 1070Ti with neocrypt algorithm