It's been mentioned, but a solo-401k would likely allow you larger tax-deferred contributions than a SEP, depending on income (Can defer ~$57k on $200k w/ solo-401k).
I have one at Fidelity, it's free and I would recommend them. Vanguard / Schwab / ETrade offer similar prototype plans.
Since you're in TN, the standard LLC + S-Corp playbook w/ 'reasonable' salary + remaining as distributions isn't going to net very much after state taxes.
You didn't specifically mention a _home_ office, but it becomes valuable if it is your principal place of business. Miles between home office and other offices become deductible. A proportional % of your rent, utilities, and if you owned the home - mortgage interest.
If you're able to max the 401k and are generally young/healthy, you could pick up a high deductible healthcare plan and open an HSA. Fidelity is also one of the best HSA accounts, so that's convenient. After age 65, an HSA basically becomes a Traditional IRA (Except for unfortunate CA/NJ residents). Some folks use the HSA as an emergency fund and pay medical out of pocket, but keep enough receipts that they could withdraw a few months of expenses if needed. (An HSA is basically self-managed, not like an FSA where you have to submit claims and such if you paid out of pocket).
If you open a solo-401k and roll your SEP into it (Fidelity supports this), you can also make a $7k non-deductible contribution to a tIRA and then convert it to a Roth. It won't lower your federal tax, but will build a tax-free retirement base (+ protection from creditors / civil suit). Can also use this as an emergency fund since Roth _contributions_ are able to be withdrawn tax-free.
(If you don't roll the SEP into the 401k, you cannot do non-deductible tIRA -> Roth conversion without paying taxes on earnings of your entire IRA pool).