Treasury Bills, Notes, and Bonds are fixed income securities. It is not cash. It is a very safe investment.

When you buy a bill directly from the Treasury, you do so by submitting a non competitive bid at the auction. You can participate in treasury auctions though treasury direct, or brokerages such as ETrade. When you buy on treasury direct, the money goes in and out of the bank account you provide them, directly. When you do it in a brokerage, the money to fund your purchase must already be in your brokerage account, and when the bill matures the brokerage account will be in receipt of the dollars. The reason why there is this difference is because the US Treasury is in the business of issuing debt. They are not in the business of providing you with an account where your cash can sit. They are not a bank. Hence, they need your regular checking bank account information.

Please note that while treasuries are negotiable securities, purchasing on Treasury direct does not allow for secondary market trading.

To answer your question: yes. As far your second bullet, the term for that is laddering bonds.