All GPIO pins except A3 and DAC are 5V tolerant (when not in analog mode), if used as a 5V input the pull-up/pull-down resistor should be disabled.
As for which pins are supported for attachInterrupt() I’m going to ping @satishgn on this. It’s not clear from the code what pins are supported, but I’d say most of them should be. There’s bound to be one or more that are not supported.
WKP is where A7 is on the Core, and does also support analog input. RX, and TX also support analog input and will be dual mapped as A8 and A9 respectively. You could access them with analogRead(RX) or analogRead(A8).
Hope that helps you along!