While starting out in PP, the SEP is the way to go. You put up to 25% of your pre-tax earnings into the SEP IRA. This lowers your tax burden for that year. In some states, retirement savings cannot be taken in lawsuits or divorces. Say you make $200k. For the first 4 years, you put $50k into a SEP. At 7% average growth, over 28 years, you’d expect that to be worth ~3.2M without further contributions. Now, you’d pay taxes on that 3.2 million, as you take it out. There is a way to convert a SEP IRA to a Roth IRA, which requires significant cash on hand. It avoids paying taxes on this when you take it out.
You’re probably not eligible for a solo 401k. However the benefit of a solo 401k is that you can contribute as an employee AND as an employer. You can technically contribute 100% of your earning as an employee. But you also have to contribute as an employee. If you employ people, as an employee you’ll have to contribute to their account at the same percentage as you contribute to yours. You’ll pay taxes on everything when you start taking it out.
As you progress, you’ll want to ensure that you’re paying yourself less, while having more business expenses. There’s also irrevocable trusts, multi tier LLCs, and FLPs for that. Maybe you don’t go on vacation using your income. Instead, maybe you happen to go to a conference in resort. Maybe your personal car is a POS, but the car your business leases for >50% business use is really nice. It’s that kinda thing.