All great advice above.
Getting started, I would recommend that if you were going to DIY, choose something that may be more cosmetic in nature. Stay away from major foundation work, major framing, etc. Learn the basics of plumbing and electrical trades. You don't have to become an expert, just learn the basics so you can have a somewhat educated conversation with someone about it. Learn what you like to do, and what you don't like.
In the long term, you will HAVE to rely on contractors if you want to scale. But if your doing a few a year, I would applaud you for doing things yourself.
Another thing I would advise, if you are going to take on a task that could cause harm, such as electrical, or HVAC, structural, etc.... make sure you take the time to educate yourself and make sure you do the task correctly. If you don't feel comfortable, either study it, or sub that portion out. There's a reason some trades require licensing.