A. Can we use previous Monero Subaddress (not the last)?.
You can reuse addresses normally, it's just not recommended for your privacy.
B. does any money that received on any subadress will forwarded to main account? or only the lastest?
It's just like in Bitcoin. Money sent on an address, stays on that address unless specified otherwise.
still don't know why some big exchange delist it.... sad
Because centralized exchanges have to follow regulations, and usually, regulations are hostile to privacy coins.
I just have to tell you that you need to change wallet software. Exodus is closed-source. Besides that you should expect minimum privacy, it is likely that it's less secure as well.