My recommendation is to stay away from ADT or other companies that want to own the equipment. It's critical that you negotiate ownership and access to all codes with the monitoring company.
Unless you're already technical enough to know what to do and how to do it, and I assume you're not since you asked here, I recommend going with a professional installation for most people - just not ADT and make sure that you own the system and that they agree to give you all codes on termination of any monitoring contract.
Many installation companies will not give you the installers or other master codes after terminating the agreement. You can usually reset the boards but that eliminates all of the system configuration. Ideally, the termination process means they go into your system, resets the dial or other connection information so you're not calling them in an alarm, and then they give you all codes - which you immediately change, including user codes. If you can't come to that agreement then the alternative is to buy a backup board when the monitoring contract starts and you can always get started again. The reason for the backup is that models change and your board may not be available in a few years. You could always get a new or different model as well.
I'm very technical and I installed my own surveillance and alarm systems. I've worked in both industries in the past and that added to my technical knowledge. But, even then, it would have been cheaper, for both the video surveillance and the alarm system, to have a professional company come in and do a basic installation. They know what they're doing, they have expertise in the specific parts they use and they know what works for what you need.
Even with my background, I found that there were a lot of new models of things and a lot of places to get them. I bought a lot of stuff that ended up not working or not giving me what I wanted so was wasted money. Because of being OCD when it comes to such things, I would have never been happy with the basic system. Both my systems are extensively customized using custom controllers such as arduinos for the security system to give me enhanced and more difficult to defeat security systems. My surveillance system includes more recording devices that a branch office of the NSA

, for both local and online storage, etc. The point is, my personality (but not my risk assessment) simply required much more than the basic system and, for my complex systems, it would have cost many times to have done over what I have in it (if I don't count the value of my time). But, if I could have lived with a few cameras covering entry and choke points and primary living and risk spaces, I could have saved a fortune on my surveillance system by just having one put in.
In my security system, if I didn't want redundant reporting options, redundant sirens that, once set off, would run independent of whether the main controller was ripped out, alarms tied to my outbuildings, lawn and farm equipment, trailers, etc., then I could have saved a ton of money on my security system by just having a trustworthy local company put it in and monitor it.
Of course both of those systems, in spite of all I have done, can be defeated or ignored by any smash-and-grab burglar with a ski-mask and stolen car or covered- license plate so, my next, and probably best, security step will be a two-layer fence system, 6-foot high, with dogs. The reason for two layers is that I don't want people building trust with the dog by tossing food when I'm not there. So I'll have an outer fence around the property (half done so far) and an inner fence closer around the house and enough yard for the grandkids to play - also half done so far). Then I'll toss in a couple of big noisy dogs in the inner fence and loud geese in the outer yard.