已知圆\({{C}_{1}}:{{x}^{2}}+{{y}^{2}}=1\)和圆\({{C}_{2}}:{{\left(x-4\right)}^{2}}+{{\left(y-3\right)}^{2}}={{r}^{2}}\left(r>0\right)\)外切，则\(r\)的值为__________，若点\(A\left({{x}_{0}},{{y}_{0}}\right)\)在圆\({{C}_{1}}\)上，则\({{x}_{0}}^{2}+{{y}_{0}}^{2}-4{{x}_{0}}\)的最大值为__________.