Any time you leave Canada before being granted your PR status on an Inland application you risk not being able to re-enter into Canada. Does it happen frequently? No, not that I have seen, however, the RISK is there and that is up to you whether to take that risk or not.
Qualification for SIN, health care and a driving license all vary.
To qualify for your SIN you want to apply for an OWP at the same time as your application. When your sponsor, in this case your husband, is approved you will then be approved in principle (AIP) and then will get your work permit and then you can get your SIN.
Health care really depends on each province. If you are in Ontario, yes, after you get your AIP you will then qualify to apply for OHIP, however it will not be in effect until 3 months after your application is made.
Drivers license is also different from province to province. Again, if in Ontario, you don't need to get AIP to qualify for a license there. You will however want to get all your driving abstracts from your state in the US so you can get a full G license, if do indeed qualify for that license. You will need 2 years driving experience, at MINIMUM to do this. I would also get a letter of experience from your insurance company on the US side. This will help facilitate your ability to get insurance on the Canadian side.
If you are not in Ontario, you would need to check on the rules and laws for the province you are in. With a screen name like Calais, it sounds like you might have come from Maine and husband is perhaps from New Brunswick? Anyway, good luck!