1. No... your MoBo and PSU should come with all necessary cables.
2. 120 GB is too small, and no, you won't miss the SSD if ya use an SSHD.... if budget is limited, we generally install a 2 TB SSHD instead of SSD + HD. While benchmarks show large differences in performance between SSds and HDs, we have done blind testing on 10 users .... 5 gamers and 5 workstation users. when we swapped the SSDs for SSHDs no one noticed.
Windows Boot time SSD - 15.6 seconds
Windows Boot time SSHD - 16.5 seconds
We have been using either an SSHD or a SSD + SSHD in every build for almost 7 years.... all are still in daily usage.
The 120 GB SSD + 1 TB HD will cost ya say $125 /... a 2 TB SSHD about $100 (1 TB = $70)...