Generally, when trying to get an I-601 approved, you need to show that not only would it be an extreme hardship for the two of you to be separated by a border-- it must also be a hardship for you to go to your wife's country. Financial hardship isn't as compelling evidence of extreme hardship. However, Ciudad Juarez has a reputation of being one of the better places to get a 601; as you live in Texas, you should be able to find a local attorney with experience at that consular post. Good luck!
If you have your permanent residence, you can apply for citizenship as the spouse of a US Citizen once you've had the green card for 2 years and nine months, and have lived in the US for at least half that time.
One possibility, if you have access to sufficient assets, would be to seek an E-1 (treaty trader) or E-2 (treaty investor) visa - Canadians are eligible for both visas.
The first option allows the individual the opportunity to conduct business between the home country and the US, and the second option would allow the individual to start and run a business - in a managerial capacity - where he or she had invested a sufficient amount of money.
Your larger issue is that you don't live together; while not an absolute bar to adjustment, it will certainly require you to prove that you have a valid marriage; her travel to visit you could serve as evidence of this. Of course, you'll need to find a co-sponsor. As to your last questions, ultimately the burden is on you to prove that you have a valid marriage; the more evidence you can provide, the better.
It would depend on whether he entered the US with a visa (and what kind of visa he entered with) and how many times he had entered - for example, did he overstay a visa and then return? Also, does he have a criminal record? Assuming that he has no bars to issuance of permanent residence, you could file a petition for your husband and then the two of you would go to USCIS for an interview to show that your marriage is a valid one.
If you have had your permanent residence for longer than 4 years and nine months, you can apply for citizenship without having to rely on the marriage that gave rise to your residence. If you file and your civil status changes during the process, simply be prepared to advise the immigration officer of that fact during the interview, and be prepared to have relevant documents at that time (e.g., divorce cert, if it's finalized by then.)
In answer to the second question: if you've overstayed your visa by more than one year, you have a 10 year bar to returning to the US, if you leave before you get your green card. Again, adjustment through marriage is going to be much easier than adjustment through your mother; you'll need to get a green card and have that for some time before you can even think about US Citizenship. So you won't be getting Dual citizenship through your mother: it may be that when you naturalize, the UK will...
Actually, as of February 2009 they're working on petitions filed January 15, 1998 so you have a long wait (See the link to current visa bulletin). More importantly, as you're here on a tourist visa, you can't wait here for the years it would take before your priority date becomes current, unless you have access to an H or L visa. If you overstay your visa, you won't be able to adjust your status here, and if you overstay and leave the US when your priority date is current, you'll likely have...