There are quite a variety of systems these days.
Possibly one of the main factors you need to think about is do you want to be able to watch live or merely record ?
I prefer to watch live and record, if so mobile display/smartphone or fixed locations maybe picture-in-picture on tv screen ?
Resolution - don't trust marketing/sales pictures!!!! - ideally see for yourself, also check under POOR light conditions especially look for clarity of faces when moving in poor light, many system look good for a static full face, when the heads are moving with poor light exposure times can be longer and all the details disappear especially on a still image taken from video!!
If lighting is poor seriously investigate infrared light source at night, quite cheap these days with IR leds so no obvious lighting. but also consider white lights to disturb or put off chancers who see an opportunity, anyone serious will have hidden there faces or have a spray can ready.
Have one or more cameras obvious, to put off chancers, but also consider a discreet well hidden camera, perhaps at ground level again IR lighting a good idea, at ground level looking upwards it gets facial images when people "hide" their faces from lights and the high mounted obvious cameras

Make sure your able to record for several days ideally one or two weeks is good, its quite well known for the serious minded thief to reconnoitre several days weeks beforehand, even come to the door on an excuse - one of my cameras is actually the doorbell pushbutton people LOOK at the button before pressing it nice full face recording !
Positioning, bear in mind where the sun is during all times of the day, long exposure to the sun will damage the camera sensors, also aperture will shut down when sun in view giving high contrast - black faces - also street lights after dark same effect, consider simple shades to block strong lights etc. that might be in view at night.