How many volts can the SLCD43 reset line take? We want to hold the reset line at 5 volts high, and set it low to reset, but weren’t sure if the board could handle it.

The RESET input is driven high (to 3.3v) by the on-board reset controller. You can drive it low through an open-collector circuit to reset the board, but you should not drive it high. If you need to, use the voltage present on J1 pin 1.