Similar to a few other comments, I use Intuit payroll (Gusto might be better in terms of UI and support) and pay myself as an employee through S-Corp. Every US freelance should structure things this way IMO, so that you can take advantage of 401k contribution and company match. You can match up to 50k roughly and that match is a business expense, so you get the money plus a deduction. As you said, this is reaping the benefits of regular employment, with the additional benefit of being able to crank up the company match in years where you make more (or can pay yourself less).

In terms of cash management, I do quarterly transfers to Vanguard which is the 401k admin. Then 1-2 times per year I pay myself a close approximation of my final S-Corp distribution (plus regular monthly payroll).