Currently I have 5.5k in my joint checking. We're in the process of moving banks and we have two old checking accounts at the old bank with 1k in each. My plan is to try and keep 5k in the main checking. I used to keep 10k and 1k as the base in mine/wifes checking accounts respectively. I've switched my wife over to using a credit card for most things, and I'm consolidating down to one shared account. So far, it's working well.
We use YNAB to track our expenses. Everything that's "On-Budget" is either a checking account, savings account (Ally), or CD (Ally). I've currently got a net positive 14k between all of our "On-Budget" accounts. A lot of that is my buffer (1 month expenses), irregular bill accumulations, sinking funds (car repairs, gifting, home maintenance, vacation), and a $1000 emergency fund. If you're not familiar with YNAB, the way I do it is divide an annual expense by 12 and allot that number to the expense monthly. The result is that when a big bill comes, I've got the money to pay for it already saved up. Other funds are things like "Vacation Funds" where I add $100 to it each month. The net result is that my fund grows and grows until we go on a vacation. All of that money that's in the budget has to physically be somewhere, and I choose to keep most of it in my checking account or an Ally savings account. It really doesn't matter where, but it should be liquid(ish). I move long term savings to a brokerage or IRA.