Hi, can't answer all of your questions, but about OHIP... you will have to give it up if you are not living in Ontario. Most provinces it's 183 nights out of 365 you need to sleep in your home province in order to call yourself a resident and keep your provincial health coverage... I think Ontario is a little more lenient, but not much.
On the other hand, you will benefit as far as taxes are concerned by really,truly severing ties with Canada while living in the US. If you maintain ties in Canada (continue to receive child benefit, use your OHIP, maybe even keep a driver's license), CRA can try to challenge your status as a non-resident and you will have to file Canadian taxes on your worldwide income. They usually spring this unpleasant little trap on you AFTER you return from living abroad.
Your Canadian citizenship stays alive as long you don't renounce it. You should maintain Canadian passports for everybody in your family while you live abroad, not because Canada will take away your citizenship, but because you'll need them for travel, opening bank accounts, getting a driver's license, sometimes to register the kids for school.
There's a government website with info for Canadians who live or travel abroad... I think it will answer your questions better than we can here at the Dis! Have a look at
http://www.voyage.gc.ca/consular_home-en.asp
And just think... you'll be living in the land of Disney! Can we visit you????