How much money should I keep in my checking account: just enough to keep up with monthly payments, or should I build it up more? No major purchases to make in the next few years.

Ideally just enough to cover monthly draws. But this is impossible - you need to be able to provide enough liquidity for unexpected draws, such as unscheduled ATM, Venmo, Zelle. Also you want to avoid overdraft. I consider cash surplus in checking consistently higher than 2k high.

My move is: Monthly bills plus like 250-300$ for emergencies. Everything else is in savings.

Save 3–6 Months of Expenses in a Fully Funded Emergency Fund

My buffer is $500 lol. But I only have 2 automatic payments of about $100 and $200. I pay my bill 2x a month (when I get paid) and I pay close attention to my finances. I'm always able to transfer money from checking account if anything should arise. And I do have $1000k sitting in a bank account with an ATM (vs. an HYSA online bank). The reason I keep the balance low is because I subconsciously spend more money when I see a higher balance. I noticed this in college and I know it still happens know. Except with bigger amounts because I can overspend by a half a grand and easily recover in a paycheck or 2 with no real impact. In college, it was $20 bucks. And I haven't had an overdraft in over 10 years, since college. I suspect my buffer will change if I have a joint account or kids. Btw, this isn't my recommendation. Just giving perspective.

You should keep 2 months of income or 3-5 grand depending on your spending habit

I leave enough of my payroll to cover monthly expense (automate transfer of payroll “excess” into brokerage and savings), plus a healthy buffer of $5-10k to allow for swings in “shit happens”

I do 2x monthly bills. I want to cover monthly autopau, and not be worried should payroll mess up. For me, this is a target balance of around 8-10k

Took advice from bill gates: have one year worth of expense in savings account.

What I would advise is to add up all of your fixed expenses per month and make sure you keep that amount (at a minimum) in your checking account. Look into your bank on opening another account(s) with no fees where you can save money. For example, I have 3 accounts with PNC: checking, reserve, and savings; and I have an account with another financial institution. Checking is used for my credit card statements, reserve is rainy day fund, savings speaks for itself, and the other is connected to auto pay for rent + utilities.

I keep enough for budgeted expenses and an additional $2k in case. I’m very disciplined in spending and so I haven’t had issues with this setup.