Is it better to instantly promote a transaction after sending? Or shall I wait some times before promoting it? And what does it mean promoting 1/5 ..2/5...?
The wallet sends 5 zero-value transactions referencing yours (as these transactions are newer, they are more likely to be referenced). When showing 1/5 it's sending the first one, 2/5 second one gets sent, etc...
You can promote your transaction instantly. In the worst case, you are wasting your computing resources (which isn't really such a "worst case", is it? ;-) )
I made good experiences with waiting around 5-10 minutes before promoting.
Compared to reattaching, you can promote as often as you want. Reattaching should be delayed at least 30 minutes.