The first thing I would do is decide what I want to automate (lights, AV, HVAC, security) and how I want to control those functions (keypad, apps, voice or handheld remote). Having clearly defined goals will tell help you if you go DIY or hire a pro.
If your needs are simple, don't mind an ongoing project, enjoy messing with the hardware and being at the mercy of the software then have fun. It's not unusual to run into roadblocks because there is no hardware that integrates with your chosen hub or no voice commands for those functions yet. Overall if you requirements are straight forward and simple DIY might be the way to go.
If you want the house to just work the way you want it to work then paying for pros to install, program, and reprogram as needed then go with a custom installer. There are well known systems like Control4, Savant, and Crestron that have many levels so you don't have to go whole hog all at once. They can be scaled up as needed. It's nice to have someone to blame other than yourself when something doesn't work or maybe even worse when it doesn't work all the time.