Seconding this! I’ve been fully self-employed for 5 years. The income/expense spreadsheets are essential to my sanity. My yearly Excel files have separate pages for each month and various tallies for each client. Accounting doesn’t come naturally to me, but once I got over the big hurdle it became routine and fairly easy.
I also learned the hard way to set aside a bigger chunk of each client payment than I expect to need for taxes. I had a couple of years in which I’d made more than expected (yay?), had therefore underpaid on quarterly taxes, and had to scramble to make up the shortfall. I increased my income again in 2017 but was able to cover the shortfall with my tax buffer so no stress!