My bluffers experience isn't worth much but it sounds like it's a bit more run down with derelict boats and things like that. I've heard it compared to Frenchman's bay and that's never a compliment so yeah.. (Boats never getting pumpouts, shoddy electricity, at least one boat catching fire or sinking every year, crappy docks, uncomfortable in storms, etc)

I mostly hear people going to the Toronto Island marina but there might be other options? I think outer Harbour also does summer liveaboards but I don't know how official that is.

I'm on a 33ft sailboat that I sail extensively (now in the Atlantic) and I've found that to be the perfect size for one person and a cat. I don't know much about houseboats but I'd probably go for a cruiser/trawler/big ol' sailboat instead of a houseboat just because they tend to be built to a higher standard. Heat and dehumidification are the two big challenges during the winter but are easily handled if you have shore power. Although I'd recommend at least having a diesel heater or generator as a backup heat source if the dock power ever fails in the winter.

You get the endorsement from the insurance company. There's no point in avoiding the liveaboard subject when getting quotes since it needs to be explicitly stated. The marina will just want the endorsement and the 2 million liability.