The resistance of the heated bed being too high can not have caused the MOSFET to burn out. Only a too low resistance could cause that.
Keep in mind that measuring relatively low resistances (such as the one of your heated bed) is difficult, and if you just used a regular multimeter it might indicate a wrong value (e.g. due to the resistance of the test ...
If there are 2 slots for temperature measurements, you don't need to solder anything, just plug the thermistor from one into the other and switch pins in the firmware. This board is basically a RAMPS 1.4 board, it includes the pins_RAMPS.h header file, so in order to switch the T0 with the T1 temperature port, you need to change:
// Temperature Sensors
I would advise against mixing nozzle - you would have many jams and clogs and you would have to use purge tower which in my opinion is not worth it. Thats scratching point 2.
Point 1. and 3. are similar to some extent. With both types you have to align the nozzles in all three axes. Crude aligning should be done by hardware and fine tuning done in software (...
It could be a couple of issues:
the heated bed tries to use more power than the ramps board is capable of because the traces on the board aren't big enough to get rid of the heat.
the thermistor is broken / not properly connected or configured, and it keeps on heating the bed forever.
a short somewhere in the wiring.
Check the wiring. If there ...
CoreXY should not require calculations which can slow down a board. Also, a normal Marlin becomes CPU limited often before 100 mm/s on 8 bit boards due to arc interpolation and other processing.
However, if you use Klipper which runs on a Raspberry Pi, 8 bit boards are rarely a limiting factor. I could print at 100 mm/s on mine with only 30% CPU utilisation ...
You can use an 8-bit controller board for a CoreXY kinematics 3D printer. The calculations are not so complicated opposed to those for a Delta.
My Hypercube Evolution uses a RUMBA controller board that hasn't failed me past years.
Late to the party but still...
The noise could be caused by the lubrication of the fan ...when you turn on the fan, the lubrication is seated down. As the fan spins, the lubrication gets all over the bearing thus centering the fan reducing the vibrations aka noise.