WELCOME TO TFL AKimsster!
First, check your local game laws. Many states do not allow the .223 RIFLE for deer. Many states have different requirements for handguns than for rifles.
And, even if legal, .223 is a poor choice for deer and out of a pistol length barrel it's less powerful than from a rifle. It WILL work, of course, but its far from optimum, and the restrictions on its performance mean there will be many shots that should be ethically passed up, where a more effective caliber would allow for a greater likelihood of a clean, ethical kill.
For optics, you have lots of options, Both scopes and red dots can do well. Scopes should be low power, 1-2x for their field of view. I have a 2-7x variable and never seem to use the high end, plus higher powers increase every tiny movement you make, making the use of a rest almost mandatory.
the option I would consider most is getting a different barrel in a more suitable deer caliber for your Contender, first.