question about classifiers

Okay, not really.  Here's the story.

I'm working on a new language, an alien language spoken by the Advena, a
race of amphibian-algae-symbiots with a penchant for peaceful (i.e.
economic) conquest.  They're the leaders of all intelligent races in the
galaxy (which ain't many) because they're the ones with the secret of
bending space-time (and thus with gravity control and FTL travel).

Their language consists entirely of verb-like words, say, "krz" "to give".
Each word has a number of possible arguments -- krz has three:

krz
1. subject
2. object
3. indirect object

A verb would be conjugated with a large number (probably about sixty or
so) pronoun suffixes.  So

krz-qa-tu-xa

where qa = "I"
tu = "any small manufactured non-mechanical object"
xa = "you"

Thus, "I give it to you."

To define what "it" is, we'd have to use another verb, for instance, "zdu"
(to read).

krz-qa-tu-xa zdu-se-tu.

"I give it to you.  One reads it."

Or, "I give the book to you."

My question is, therefore, if I'm going to have these fifty or so pronouns
but no nouns, how did these pronouns evolve?

The only theory I have, really, is that there might be a verb form, say,
"etu" "to manufactur", and thus "tu" becomes "a manufactured thing."  But
why wouldn't it just become a pure noun instead of a pronoun?

I can argue because they're aliens their minds work differently (and
Advena minds *do* work differently -- they can multitask on three
different levels, for instance).

In Earth languages with things like classifiers (you know, like in Thai),
how do these words evolve?  Are they just worn-down forms of the thing
they clasify?  Or are they separate words with their own evolution?  And
how would the Advenae develop classifiers for things like "space crafts"
or even "mechanical object"?