Dose is a unit.
Dosage is a rate.

The examples you found use "trouble" as a verb. Your question is about "trouble" as a noun. The rest of the sentence is an adjective phrase describing what kind of "trouble" and requires a gerund, not the infinitive.

The reader is not right, not even technically. If I talk about "my teacher," do I really need to clarify that the person is not a slave?

"I'm just saying" is a hedge, but you're right: it usually comes with a helping of sarcasm that marks it as understatement. "—is what I'm saying" can also be a hedge to keep the preceding statement from crashing down with emphasis. It can also be a manipulative tactic for time, because it prevents the hearer from responding immediately to the main point.

There is a practice among some English dialects of using a singular noun in measurements. For example, an English person might describe their weight as "10 stone." Perhaps it comes from the adjectival form, such as "I made a three-egg omelette," where the noun is never plural. As to your marketing question, pick the version that you think would stand out. How about "Too Egg"?

The word "so" is used in different senses in your examples. In the first, it is an anaphor relating the second speaker to the first. This usage requires inversion. In the second example, "so" is used to indicate agreement in the sense of "thus."

There is no need to put quotation marks around a capitalized acronym. The capitalization already makes it stand out.

The core of the sentence is "I find a store." The rest is a relative clause that says something about the store. The two can have independent tenses.

"I found a pet store that sells ferrets" implies that the store sells ferrets in the present.

"I found a pet store that sold ferrets" implies that the store has sold ferrets in the past but does not necessarily sell them now.

Yes, it appears to be approaching vogue level and has increasingly grated on my ears lately. I first encountered "Germanic str" in a series of YouTube videos narrated by a Brit and put it down to a regional quirk. But I am hearing it elsewhere now in a variety of dialects. Something new to add to our basket of nettles along with creaky voice, "literally," "step foot," and "beg the question."