While not directly related to RSS, Polish Central Bank provides currency rates for most popular currencies via XML (it’s in Polish, I was unable to find instructions in English). I think this may suffice.

Technically this was supposed to be a replacement for RSS channels but most modern readers seem to support both standards now.

Yes, they can be safely deleted (I have installed some replacements from Fossify afterwards). And when it comes to the launcher I use Kvaesitso.