Suffix -ar in IE and Vennemann's Vasconic

[Eduard Selleslagh]

Not being an IE-ist myself, I would like to ask the knowledgeable people on
this list for more (IE) information about the suffixes '-(t)ar' and '-ar'
which exist in both IE and in Basque, apparently with roughly the same
function and meaning: the former is an ethnonymic-forming device (with 't'
after final vowel), while the latter can have a series of meanings, often
expressing occupational relationship with something, or something more
difficult to describe in a general way (e.g. collectivity, multiplicity).
Apart from the non-IE Basque, the languages that use '-ar' frequently and
productively I am aware of, are Slavic (e.g. Serbo-Croat 'put/putar' =
'road/road worker'), Albanian (e.g. 'Shqiperia/Shqip(e)tar', 'Albania/ (an)
Albanian'), (I'm not sure about other satem lgs.like Indo-Iranian) and maybe
Latin (ending -arius and -or(?)). In Germanic there are various suffixes
like '-er', at least in some usages (e.g. Londoner, painter(?)), that might
qualify.

For those who believe in Vennemann's 'Vasconic' substrate theory, this
cannot be a coincidence, but my questions are not really about that:

1. What is the Proto-Slavic form, or forms if the -ar suffixes in various
usages are not the same?
2. What is their reconstructed PIE form?
3. What about the Germanic -er (one or more)?
4. What about Latin -or (actor) and -arius (and -alis, -aris, etc.)?

Ed. Selleslagh

[ Moderator's comment:
  Latin -tor is cognate with Skt. -tar "agent, actor", Hittite -tar "idem"; the
  suffix is not "-or".
  --rma ]