So, now that I've taken the step into holding the treasuries myself through the Vanguard Bond Desk, I wanted to ask those with a similar experience: Did I do this right? Heck, it seemed almost too easy once I did it. Here are some screen shots from my VGuard Bond Holdings (account info excluded).
Bond Holdings Overview:

Long Term Treasury:

These I sell in approx 10 years - when they are 20 years to maturity date. Have that correct?
Short Term T-Bills:

These (1 year T-Bills) I let mature, and use the funds to purchase another round of 1 year T-Bills. Have that correct?
I've done some reading but I need a little clarification on how the pricing/maturity of the T-Bill. Each day I see a change up or down in the value of the Long Term Treasury, but not the T-Bill. Why? I'm still a rookie at this, so wanting to make sure I'm doing this right as I will need to make another LTT and T-Bill purchase soon to balance the PP.
Thank you for the help.