A1) Sale of Rural Agricultural Land will not attract Capital Gain Tax because Rural Agricultural Land is not a Capital Asset u/s 2(47). However, be careful because Income Tax has it's own definition of rural agri land, in which it should not just be within rural vicinity, but it should also not be located at a certain distance from the nearest municipal area.
Rent received from agricultural land would constitute agricultural income, and would therefore be exempt from tax u/s 10(1). But you're still expected to report such income if you're also receiving income from other sources. This is because if agricultural income is not your only income, then tax has to be calculated using a different method which requires the exact amount of exempt income. So there is cause for concern to that extent.
A2) I think Rent would be declared in the year of accrual, and therefore declaration in FY2020-21 seems more appropriate