A very large amount of my business (>90%) originates from online leads. Most from social media, some from lead generating web services. (Home Advisor, Thumbtack.com, etc, etc...).
I built my own website because that is what I have done for years. Although it's not my best work but building and maintaining a fantastic website take a LOT of time. When most of my time is devoted to other ventures to increase sales/revenue. As it should be.
Really, the websites sole purpose is to build legitimacy in my brand. I get so few leads from it that it's not even worth mentioning a total/average. I hope that increases with a recent redesign but I wont hold my breath.
Your focus as for web presence should be on google and
yelp and other major search sites. Get those solid and then focus on social media. Having a facebook page has brought in more (free) work and interest than any other avenue.
Once all that is set up, you can pay someone to maintain the SEO
for you but that is totally up to you but it's advised.