"l" and "n" suffixes in some IE ethnonyms?

I've been trying to figure out the PIE forms and developments of some suffixes that seem
to crop up in numerous IE ethnonyms. There are various names with endings reflected in
(mostly) Latin sources as -ones or -oni (perhaps depending on whether they are treated as
n-stems or o-stems? or whether they were adapted from Greek sources?), as well as some
appearing as -ani. Names with -ones and -oni seems to crop up in Italic, Celtic, and
Germanic contexts; I'm less sure about the distribution of -ani?

What's the origin here? Is this from the Hoffman suffix -h3o:n? (That would give a long
/o:/ in Latin, I think, a short /o/ in Celtic by analogical leveling, an /a/ in Germanic
reinterpreted as an /o:/ by Latin writers by analogy?).

Meanwhile in Italic contexts, there's this -uli suffix that keeps cropping up. I'm thinking
this might be a PIE or Proto-Italic -elo:s > -olo:s > -uloi > -uli:? Might this be related to
other Latin derivational suffixes in -ilus, with the same original -el- becoming Latin -il-
under different phonological conditions?

I'm guessing around at this based on eyeballing names in classical sources and a very
limited knowledge of the linguistics. (Are them, BTW, any good resources online or in
print that discuss PIE derivational suffixes?)

Cheers,
Carl