i might be able to help with #1 if you are willing to do a compile! the stock firmware does have a super straightforward build script and compiles quickly. you can change the mouse button positions in the stock firmware in main.c around lines 480-485, the last numbers (4, 8, 7, 3) are the only one you’d need to change.
to swap scroll and middle, you’d want:
static int tb_btn_scroll_idx = KBD_COLS*5+3;
static int tb_btn_middle_idx = KBD_COLS*5+7;
there’s also my QMK firmware port if you’re interested in that. setup is a more involved and compile takes way longer (especially if you’re on IMX8MP) compared to stock, but it does make the mouse row a normal part of the keymap so the keys are easily reassigned without sifting through boilerplate code. if you go that way you can set the bottom row like this:
MNT_SCRL, MS_BTN1, MS_BTN3, MS_BTN2