I have a SEP-IRA from self employment. The contribution limit rules are very confusing to learn thoroughly. Yes, most of the materials from the IRS on SEP-IRAs say 25% is the max employer contribution, but you're both the employee and employer which makes for some very weird rules when you actually get into it. The end result is the effective max is 20% of your net profit from self employment minus the deduction for half the self employment tax.
A SEP-IRA is very easy to set up; aside from opening the account with Vanguard or whomever, you have to fill out one simple IRS form and keep it in case you ever get audited. That's it.
The downsides to a SEP-IRA are the contribution limit and the fact that it's an IRA, so you will have problems doing backdoor Roth contributions if that's something you're interested in. Your other option is an individual 401(k) which I'm looking into this year, but it's much more of an administrative burden. For more, see
http://www.bogleheads.org/wiki/Solo_401k_planWith any of these accounts, MAKE SURE YOU DON'T CONTRIBUTE TOO MUCH. Since your contribution limit depends on business income (which can vary month to month), deducted expenses, and self employment tax, it can be easy to mess up. If you make contributions throughout the tax year, keep them low to make sure you don't put in too much. You can catch up as close to the limit as you want at the end of the year, once you know what your Schedules C and SE are going to look like.
All of this is doable and it doesn't absolutely require a CPA if you take the time to learn the rules and tread carefully.