think the only problem will be obtaining the reliable 'ppp device' for amiga. unfortunately,
those things were not free, so you'll need to do some searching..
for some reason, I had used amippp.device instead of ppp.device, maybe its more reliable.
anyway, when you configure, if authentication doesn't work, disable everything (on both server-mikrotik and client-amiga) except PAP.
edit:
found this site:
http://www.davidfong.info/newton_tcp_Amitcp.htmlhmm, it says ppp is better than amippp.
edit2:
you also need a good serial.device, I've used artser with 38400bps.
baundbandit is supposed to be best, but iirc it wasn't very reliable.
what CPU and KS do you have?