For multi-emitter TTL inputs (commonly found with 74, 74S, 74LS, and 74ALS, for example), cannot tolerate higher than \$5.5\: \text{V}\$ at their inputs. So the minimum resistor size that is used for unused inputs must be based upon the maximum peak voltage at startup that may occur. If your power supply might peak up to say \$7\:\text{V}\$ before settling back down to \$5\:\text{V}\$ then you must have a resistor of at least \$\frac{7\:\text{V}-5.5\:\text{V}}{1\:\text{mA}}=1.5\:\text{k}\Omega\$.
Meanwhile, the input must be at least \$2.4\:\text{V}\$ to be seen as HI, so this means the maximum resistance is, assuming a minimum \$V_{_\text{CC}}\$ of \$4.75\:\text{V}\$, \$\frac{4.75\:\text{V}-2.4\:\text{V}}{N\,\cdot\,I_{_\text{IH}}}=11.75\:\text{k}\Omega\$ if there are \$N=5\$ inputs being serviced by the resistor and if \$I_{_\text{IH}}\approx 40\:\mu\text{A}\$, for example.
The above is assuming you want the inputs tied HI.
Finally, all parts of an IC must be connected. Even if you have, for example, two FFs in an IC and are using only one of them, you must make sure that the other unused FF has all of its inputs tied somewhere.