Your understanding is mostly right
“A 到 B 了” means "become so A that have got into the condition of B"
- A: adj, but used as a verb, which means "become A"
- B: a condition
"只能吃土" is a 状态 (condition) so it is the same as "只能吃土的状态"。
"到~" means "getting into" a 状态.
"了" means finished. There might be no "了", depending on the tense.
Correct example:
- 我很穷，（已经）穷到只能吃土了
- 我很穷，（已经）穷到只能吃土的状态了
- 赌博会让你 穷到只能吃土
- 赌博会让你 穷到只能吃土的状态
Is it in fact a structure to create such sentences?
Yes
只能吃土的状态了 - I don't even know if I should treat it as a sentence or as a noun. So: what should come after 到?
As discussed above. 只能吃土的状态 is a 状态 which is a noun. 了 is following 到 indicating the tense.
Is this sentence correct? 累到不会走路的状态
Correct, but not a complete sentence. Missing subject and tense indicator.
Is this sentence correct? 累到不会走路
Correct. Same as above
What's the difference between 穷到只能吃土的状态了 and 穷得只能吃土?
In 穷到只能吃土的状态, 穷 is an adj. but used as a verb, followed by the extent of this verb.
In 穷得只能吃土, 穷 is just an adj. followed by an adverb.
Both are correct and mean the same.
