How important is timing? If the grass gets a little high, is it ok for a few days or do you pride yourself on an immaculate lawn? After you answer that consider your schedule. Is it realistic to find time in your schedule to mow once (or several times, depending on a variety of factors) a week? Does paying a neighbor kid or professional service to take mowing off your plate make you relax a little, or make you more anxious?
Many of the same though exercises apply here too. What kind of time are you willing to put in? In addition, You’ll have to ask yourself if you’re okay with not having great results the first time around. Reseeding especially takes a lot of research, trial & error, and patience. The potential to use too much or not enough of one thing or another is always there for newbies. You may have to wait until next year to make your corrections and try for round #2
This is a quick answer. Just hire an experienced professional. The amount of trade skill, knowledge, and experience that goes into most hardscaping projects is enough to make your head spin. Not to mention potentially dangerous without the right equipment that can only be driven by certified professionals. Be smart, be safe. Invest in quality work.
As with any project, you will always have to consider the Venn diagram in the image above. Which factors are most important to you? What can you sacrifice in the name of completion? Find where your priorities lie, and the answers will become clear to you.