*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 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*.