Hello. I will happy to assist you with this.
Typically, each floor supports itself only. Is that not the case for your home?
2x8 going 21' are incredibly undersized. You need 2x12 as a minimum, and that is with a good species and grade.
The rest of the questions really look like they require a sketch or framing plan to understand.
Can you post a sketch for me to look at so I can be sure we're on the same page.
It appears the maximum joist span is approximately 11'-6". That will require a double 2x6 doug-fir no. 2 @ 16" o.c. if you don't have ceramic tile. If you do have ceramic tile then you will need a triple 5.5 2.0E LVL @ 16" o.c.
Hello. Do you have any other questions for me on this topic? If you could rate my answer, I would appreciate it.
Hello. Do you have any other questions for me on this topic? If you could rate my answer, I would appreciate it. Experts are credited for each appropriately rated answer.