Quo is (based on) a relative pronoun, but it is used cataphorically: quo refers forward to eo.
A similar construction you will be familiar with:
Eam, ex qua natus es, caedes.
"Her, of whom you were born, you shall slay."
This can be reversed:
Ex qua natus es, eam caedes.
"Of whom you were born, her you shall slay." (This word order is strained in English, but perfectly fine in Latin.)
Caedes ex qua natus es.
"You shall slay of whom you were born." (We'd normally add an explicit antecedent "her" here in English, but, in Latin, this is less necessary.)
So ex qua...eam here is the same construction as was originally quo...eo.
I suspect the 'postcedent' eo is less required in poetry, but I'm not sure about prose. The relative quo cannot be omitted.
Do not be confused by English "the" in "the more, the better": this is a very special use of the article, a kind of parallelism perhaps, which is typical of English, but not normally possible in Latin. The Latin language uses adverb/demonstrative + conjunction/relative instead: quo...eo, cum...tum, ita/eo/tantus/etc...ut, tam...quam, tantus...quantus, tot...quot, talis...qualis, is...qui, etc.
Plus...plus: this kind of parallelism is also uncommon in Latin: I do not think this is possible. Constructions like alius...alius, "one...the other", are limited, and of a slightly different kind.
Instead of eo avare, you should use the comparative, eo avarius.