Question Feedback on my upcoming built

What is the purpose of this build?
From the graphics card, I might presume gaming.
A balanced gamer will budget about 2x the cost of the processor for the graphics card.
You are spot on there.
Unfortunately, scalpers and supply constraints have made a mockery of getting any of the new cards at anywhere near to MSRP. And, they are out of stock everywhere.

What kinds of games will you play?
Do you now have a monitor?
At what resolution?
It would gall me to pay $800 for a 3060ti with a MSRP of $400.
A quick look around shows high end graphics cards out of stock everywhere.

Your best bet might be to look on ebay for a rtx2080 or similar.
Tom's gpu hierarchy chart will give you an approximate ranking of cards.,4388.html

If you have aspirations of gaming at 4k resolution, then a 3080 class card is in order.
OTOH, if your resolution is 1080P, then much less is needed.

But, you need a graphics card.
If you can order a 3000 series card, you may be told your card is on back order with no estimate for availability.
Buy only when you can confirm that the card is actually in stock.

If you play fast action games, then the graphics card is all important.
If you play cpu centric games like sims, strategy and mmo then the cpu, particularly single thread performance is most important.
I don't know what to tell you.

On the cpu, if you need fast single thread performance, the new ryzen 5600 is a winner. Not so much for the clock, but for the improved performance per clock.
Unfortunately, that is also largely unavailable.

I would consider the intel i5-10600K as an alternative.
Here is a review:
It compares favorably with the 3700X at less cost.
As a plus, the intel processors will include integrated graphics which would give you desktop capability until you can buy what you want for a graphics card.
The K suffix processors need a cooler, Air will work well with your case.

I would not buy a HDD today unless it was to store large sequential files such as videos or backups.

On a budget, look at the 1/2tb intel 665P or 660P m.2 nvme drives
It is easy to add storage later if you need it.

At 2tb, look at a samsung 970 evo plus for best performance.

On the power supply, 650w is fine.
The seasonic S12II is an older tier 4 unit on this list:
I would try for a tier 1/2 unit, no less than 3 that has a 7/10 year warranty.
A quality power supply is a long term investment that will be good for several upgrades. They do not go obsolete easily.
I would look for 750w.
A psu will only draw the power demanded of it, regardless of the max capability.