Understanding strategy behind buying T-bills/Notes/Bonds

Hi all,

I wanted to understand the strategy behind buying T-bills/notes or bonds right now. Pls let me know if I'm missing something, I read many ppl in this sub are buying t-bills. Want to understand the reasonings..

Currently HYSA like Wealthfront pay 4.8%, but that is not guaranteed. They can increase/decrease it in the future as per Fed's interest rates.

1. So is it better to buy a T-note with maturity of 1-2 years or maybe even a longer term horizon such as 5-10 years because in that we are guaranteed the interest rate for longer period of time? Even if fed lowers interest rate in near future, the return on these t-notes will stay the same until maturity?
2. Is there any benefit of buying directly from Treasury direct instead of someone like Schwab? Maybe selling the t-note at higher price is easier at treasury direct? (If Fed lowers interest rate, then the value of the t-bill/t-note will also increase. )