I'm looking for a right way to stress words ending in -fluence in American English. There should be a change of stress depending on whether it's used a noun or verb. Also, in "finance" I stress the 1st syllable as a noun, but 2nd as a verb - am I right?
The word finance can have stress either on the first syllable or second, whether it's used as a verb or a noun. I happen to work in that field and I stress the first syllable unless I'm trying to impress someone, in which case I use the second. Stressing the second syllable sounds fancy almost to the point of being supercilious.
Influence has the first syllable stressed, always, regardless of whether it is used as a noun or verb.
Confluence is an uncommon word to the point that most people won't know it (except because of context) but the first syllable is stressed there too. I wouldn't be surprised if people mispronounced it. I've never spoken the word aloud.
I don't know what other words you might consider "similar" to these but stressing the first syllable is a good guess in the US.