2) For sure the Uno Wifi WON'T work with the Uno wiring. This has been the issue I wanted to clearly document here, since most of the available documentation has been written having in mind the Uno board, NOT the Uno wifi... unfortunately...
the documentation was written before the Uno WiFi Rev. and other boards existed.
in general for SPI the SPI header should be used if available. other boards including Mega or Leonardo don't have SPI on pins 11, 12 and 13, but the SPI header is the same.
and the new Nanos (Every, 33 IoT and 33 BLE) don't have the SPI header but have SPI on pins 11, 12, 13 as the classic Nano.
If the SD adapter has a level conversion IC for 5 V boards, then it should be powered with 5 V.