A Pro Mini should work fine. The 3.3V version does not require any level shifting.
Paste your sketch in a CODE window or attach the file. Are you just wanting a line that moves or a filled semi-circle that rotates?
You generally get the most responsive display if you just erase the old triangle and draw the new triangle. Most changes are incremental. i.e. a thin triangle.
Post a link to your actual display. There are several 128x160 controllers. I have a sketch that will diagnose which one you have.
David.