No strings attached to the accounts themselves. The only time there are some strings is if they have a sign up bonus. Those require you to keep a certain amount on deposit for a certain period, like 90 days, to earn the bonus. But for the account itself, nope. Most have no minimum balance and no fees.
There is a limit of 6 withdrawals or transfers per month, but only if they are initiated in that account. For example, if I make a transfer from Ally to Vanguard, that counts as one of the six. But if I initiate the transfer in my Vanguard account to pull money from Ally, that does not count.
All of that said, I'd also suggest you consider other options. Depending on how much cash you're talking about and how liquid you need it to be, you can do better with short term treasuries. Right now, Ally is paying 0.5% but you can buy a 3-mo treasury paying 0.8%, a 6-mo at about 1.1%, etc. If you don't need to have immediate access to all of the money, you might want to spread it around a bit.
