About this database conversion that IPB is suggesting me... Are there any risks? Is it possible that something won't work after the conversion? And how long would it take for a ~8 GB database?

I tried it on my test board and for some reason it couldn't finish. By looking at the database after that I had some tables converted and some not. After that the search did not work at all, but I haven't tried rebuilding the index. Anyway, it is not totally harmless.

YMMV