It's a good thing this is an international, not a UK-only forum, then, AC-DC.
Bing, you're right that some floatplanes you see that appear to have wheels are just on dollies for taking them out of the water. The floats with wheels underneath that can be used for landing on runways are called "amphibious floats." The wheels are retractable: up for water landings, down for runway landings. Yes, they have brakes; steering on land is by rudder and differential braking only. Sorry, I don't know the comparative crosswind limitations of amphib and wheel-equipped aircraft, but I imagine that amphibs must to meet the same minimum crosswind standards as other aircraft.
Amphibious floats are available for many types of aircraft, but you need quite a lot of power, and will lose some useful load in the conversion. A C172 on normal floats is seriously underpowered, so an amphib C170 sounds unrealistic. I've seen C185, C208 and lots of Beavers on amphibious floats.
Amphib aircraft are also ridiculously expensive to insure, as if you extend the wheels for a water landing, you're going to flip and thus seriously damage the entire aircraft.
The name in floats is EDO. Some pilots call all aluminium floats EDOs. I can't find a web page for EDO itself, but Kenmore Air is a big float operator, and an EDO dealer.
<A HREF="http://www.kenmoreair.com/edoindex.html" TARGET="_blank">http://www.kenmoreair.com/edoindex.html</A>
While looking for an EDO site, I found these possibly useful links:
<A HREF="http://avstop.com/Stories/BuySeaPlane.htm" TARGET="_blank">http://avstop.com/Stories/BuySeaPlane.htm</A>
<A HREF="http://www.seaplanes.org/" TARGET="_blank">http://www.seaplanes.org/</A>