ok for the axe. t8f (8mm scooter google it)chains work great for a scooty axe they have bean proven to work and can take the power. For ESC i suggest time THIS it is the replacement for the tz85 and it best ESC which is still in procduction. i would suggest a Feathertwo Single channel but they are out of production and people who have them are not that willing to sell. on the Arduino front i did dabble with the idea but speaking to Shakey it is a bad idea as the Arduino can get confused and fire the weapon randomly. the only person i know who has used a Arduino in full combat is Rory Charlesworth in Aegis acting as a limit switch controller.
For drive 550rpm sounds really low so either you are looking at beetle gearboxes or a really high reduction, you got a link to them ?