I'm a bond novice seeking help

[whatthehey]

I'm ok in equities and general financial economics but I've never followed bonds at all and find online resources like investopedia assume basic knowledge I lack.

I have a decently diversified 401k including some in income bond funds. I have a small day trading account all in equities, a likewise modest amount in long term dividend paying equities and enough cash cushion to live for 6 months if needed.

What is missing there is as near riskless as possible long term investments that pay a bit more than savings accounts as I start looking to retirement (I'm 51 but hope to be done before SSI age). In theory that cries out for 30 year treasuries with some low risk corporate bonds maybe leavened in.

I much prefer self-managed rather than funds. My questions are admittedly rather naive but maybe I can get started here.

I'd like if possible to say buy $20k of 30 year treasuries and then add perhaps $1k a month to that, accelerating as expenses allow, and keep reinvesting interest payments until I need to withdraw. Is it possible to directly buy 30 year treasuries in such low amounts and if so how?

Really stupid question but it's amazingly one not covered in reference materials I can find. My assumption is that if I buy 30 years now paying a bit under 3%, then if prevailing interest rates rise so do my yields. Is this true or do they act like fixed rate CDs?

If I have to go with funds, which I suspect as I can't easily see any easy link to retail treasury buying opportunities, what are recommendations for very low load options?

Thanks all.