This forum is full of stories from people who tried to do it themselves and ended up fouling things up. Of course, if there are any business owners who are successfully administering their own plans, they probably aren't coming on here to tell us about it, so you do kind of have a self-selecting group.
That said, I would strongly encourage you to hire a TPA. For a one-member LLC with no employees, you won't have any testing and won't even need a 5500 until combined plan assets go over $250,000, so prices should be pretty reasonable, and you have the confidence of working with an expert who knows all the rules.
For the cash balance plan you are required to use the services of an enrolled actuary even if you don't have to file anything, so there's no doing it yourself with that one.
If you can tell us where you're located, I'm sure someone on this board will know a local TPA who can help you. Our company for example does administration for dozens of owner-only and micro-sized plans so there are definitely firms out there who cater to your market.