Hi
For XIAO nRF52840 has a dedicated battery charger BQ25100 for the BAT+ and BAT- pin, which could used for charging 1 cell Li-Ion/Li-Polymer battery.
Q1: It support to charge 1 cell Li-Ion/Li-Polymer battery which the Battery charge voltage (Max) is 4.2V
For Q2 and Q3 I do not understand what your are looking for.
Q2: You have mentioned 800-1000ma current rating for what is purpose and usage?
Q3: Use a rechargeable magnet/induction plug on the XIAO for what is purpose and usage? is it for supplying power to XIAO?
Please check the datasheet of the bq25100 chapter 7 Specifications, it listed out the ratings about the charging chip.