The front panel is removable and can be replaced with a BPI-R4 panel at any time.
Furthermore, a board can also additional be installed on the left side (e.g. for redundancy). Then there is a front panel with openings on the left and right side.
All combinations are therefore possible
1x BPI-R3 or
1x BPI-R4 or
2x BPI-R3 or
2x BPI-R4 or
1x BPI-R3 & 1x BPI-R4
let's stay in touch, I don't think that should be a problem.
This is a good alternative to the APU boards from pcengines,
as these are no longer manufactured
Yes, that is also an option. But then you have a large gap between the board and the metal case, if you want to use the onboard power connection. The use of an additional aluminum block with thermal pads, to close the gap, would then be optimal.
I deliberately refrained from routing the serial connection to the outside. This makes it more difficult for a unauthorized access (without authentication) from outside.