When I've finished this course.... and When I finish this course...
are both accceptable, but - as I hear it - the present perfect focuses more on the event of finishing: 'When + past perfect...' suggests 'The moment I've finished - the day after I get my results - I'm going to...'. Using 'The minute' in place of 'When' reinforces that suggestion. On the other hand 'When + present' suggests 'Some time after I finish - maybe I'll take a year out volunteering in Africa first, but eventually - I'm going to....
But (and this is not a matter of personal preference or perception ) 'When I will finish...' is just wrong.
- For Teachers