1)1050 Ti is not a worthy upgrade over a 1050. You must get a 1060 or a 480/580 at least to make a meaningful upgrade. If I were you, I'd wait for the release of Volta GPUs. After all, the 1050 can run all modern games (at medium settings if not high) and any upgrade is not worthy with the release of next gen GPUs within 6 months (probably).
2)An i5 is better than an i3, but is not better enough to be a compelling upgrade. But the i3 may be a bottleneck in some games. Upgrade to i7 or don't.
Also you may need to upgrade your PSU in case of GPU upgrade.