There is a bit more complexity to defending a DUI than merely accepting at face value the reading of the breath test. Depending upon a number of factors, you may not have been impaired at the time that you were driving. Consult with an attorney who is knowledgeable in the specific area of defending these types of cases.
DUI cases are almost always more complex than they first appear. So in answer to your last question, if it is something that you can afford, retaining counsel in advance would be advisable. Additionally, you can anticipate being charged with a refusal, along with the underlying DUI charge.
You are correct that neither the Field Tests nor the sense of smell is an accurate measure of the per cent of alcohol. But along with the driving through the stop sign, they are all supportive of probable cause.
I don't know that there are actual numbers available to answer your question accurately.
Some attorneys handle both the criminal aspects as well as the administrative, some have a separate attorney handle the administrative aspects, and some, like the public defender's office, do not address the administrative type matters.
You need to speak with each individual criminal defense office that you are considering and inquire specifically if they also handle administrative and licensing...
From your question, I am not exactly sure whether your upcoming appearance in January is your first appearance or not. If so, you may be expecting something to happen before the time that it actually can. There is not much that your attorney can do for you until that first appearance.
Yes, some people have been turned away for a prior DUI, which the Canadian Government apparently takes pretty seriously. It depends upon what they ask you, because some individuals have not been questioned and have gone right through. Some, in the face of being turned away due to a prior DUI, have been able to pay a $240.00 rehabilitation fee. It is apparently a bit dicey up at those border crossings!
You already have one. It is called the public defenders. They are the institutional equivalent of pro bono attorneys. If you did not have your public defender, and had to go out on your own to find a pro bono lawyer to handle a first degree murder case, you would probably appreciate your public defender much more.
You definitely do not want to go through this process without the advice and assistance of counsel. And whether it by an attorney that you have retained on your own, or by a public defender, if you qualify, based upon your low income, you definitely want an attorney representing you. To many individuals look back on trying what you are suggesting, and in retrospect, wish they had been represented. Don't find out after it is too late.