I used Simplisafe for my entire home alarm/security system and loved everything about them. You can add components as you need them and skip the ones you don't need.
I love our Arlo Pro 2 system. Wireless, great quality, and the batteries last for six months. If battery life is important to you, be sure to get the Pro 2 (not the Pro 3) since it lasts twice as long.
Another vote for Ring. We have a camera/floodlight device, and the doorbell in addition to 6 path lights. Having all of those linked up and to be able to manage it all so easily is wonderful. We plan on extending our devices with them soon.