curmudgeon- Thank you for pointing out that Ryanair doesn't fly into Marco Polo, I hadn't realized that. I haven't bought the tickets yet and now I'm wondering should I fly BMI instead as it goes from Heathrow to Marco Polo?
We'll be in London for two days before we fly to Venice and I'll have an all zone tube pass and I can always buy tickets for the Stansted Express so I wasn't worried about getting to Stansted.
However, now I am more nervous about Venice as we don't speak 1 word of Italian other than Vino!
BMI is £100 as compared to Ryanair at £58. Is it worth it to fly BMI for the convenience of Heathrow/Marco Polo?

It's a bit of a tossup. I've used both Treviso and Marco Polo, and I don't have a strong preference either way. Treviso is a very small airport (the 3-4 ryanair flight must make the bulk of the traffic), but small can be convenient as long as you don't need shops and car rentals etc.

When we flew ryanair, we got tickets really cheap (though you need to track all the taxes and surcharges; they can be more than the ticket). I'm a little surprised that they already have March prices up. Ryanair (and easyjet) pricing is widely variable. I think the train to Stanstead is about 15 per person each way.

Venice is very much a tourist-oriented city, and it is quite easy to get by there with just english. The vaporettos can be a bit confusing at first, you need to be aware that the major stops will actually have several docks; you need to check the signs so you go to the right dock for the vaporetto line you need (also, some of the routes change at night).

I've gotten a response back from the Locanda Fiorita for 105 euros/nt. for March including breakfast and taxes.
Does this sound fair or should I wait to see if they will offer winter specials later in the year?

If you're researched Locanda Fiorita and like it, I'd guess that 105 EUR is a very good rate, especially including breakfast and tax.

I'm very happy with the rate, just wondering if I can do better. My gut instinct tells me to book it and shut up as it's a small inn and will only sell out the rooms if I take a chance.
Just booked air on BMI. Decided to pay more and go from Heathrow to Marco Polo. The flight into Stansted wouldn't arrive until 1am and that created problems on the return trip to South Kensington.
Thanks for everyones input. I'll let you know for sure which hotel we choose and our critique.

Early March is still pretty much off-season, so rates are definitely much lower. I don't know the specific hotel, but the area is fine. I wouldn't worry about hurrying for reservations (except at a couple of the guidebook favorites like la Calcina). Be aware that at some hotels, some of the cheaper rooms will have bath down the hall (Fiorita looks that way); you need to specify en-suite if you prefer your own bath attached to your room.

I did a quick check, and you can get similar rates (or for a bit more, a gorgeous view) at the Wildner, at least until March 16.

http://www.veneziahotels.com/uk/w_description.htm