Chosen Solution
If I buy one with 1TB, can I later upgrade to 4TB?
Sadly, its not technically upgradable. Review the iFixit teardown 2021 MacBook Pro Teardown: A Glimpse at a Better Timeline The flash chips are soldered to the logic board and would require someone with very deep skills to properly remove the chips and then locate the needed replacements (if that is even possible, Apple might have locked in on the supply) and then solder them on. There is a huge risk here as the act of removing the chips could damage the logic board and if not done properly it may appear to work but over time the soldering job fails! Lastly the cost would be prohibitive as well. Bottom line: Buy the biggest SSD drive model you can afford and forget about upgrading this system internally.
