Brad,
Changing to floats the first time is a day and a half to two day job for an experienced crew. After that, the swap is a half day deal for a good crew. Just two people: Full day job if you know what you're doing.
You need a HOIST, preferably INSIDE a hangar to lift the plane. Doing this outside in the rain and wind is a bitch--trust me, been there, done that a number of times. If on straight floats, you need to have some means to launch that seaplane, after the floats are on it, and to return it to the hoist at the end of the float season. A hangar at an airport next to a lake or float pond is ideal. Launching off a trailer works okay, but then you have to have a VERY nice grass strip to land on at the end of the season, and a forklift, or?? to carry the plane to the hangar. In float country, there are generally lots of options of airports with float facilities, that do this kind of change-overs all the time.
As to time in type, ask your insurance company. Are you talking about operating for hire?? Look into the Canadian requirements for that. You'll likely have to pass some sort of proficiency check, like a 135 checkride. Insurance companies generally have a specific requirement on floats, and expect your insurance coverage to double or triple UNLESS you are operating for hire, in which case, good luck. A low time float operator operating for hire is going to be a very high risk insurance-wise.
I can't tell you how much flying it will take to become "competent". There are lots of ways to get in trouble on floats, largely because the PILOT makes almost all the decisions: Where is the runway, how deep is the water?, how much wind, and what direction?, etc. etc. It takes a while to learn to work the airplane efficiently and safely, but it's something you can do, if you just start CAREFULLY, and don't get too carried away with yourself too soon.
If you're going to do this, I'd find someone who can work with you and give you a THOROUGH checkout in the 185 on floats. That's a lot of airplane for a float newbie, but a good checkout will get you going down the right road, at least.
Used floats: Edo 3430's are probably the best older floats. If you can find used Aerocet 3500's, Wipline 3000 or 3450s (none of which are very old). If you're working it commercially, that is. Recreational flying: EDO 2960's work fine, but you need to find a check out airman who KNOWS those floats well, or CAP 3000's are great floats, with the same proviso.
I'd stay away from first generation PeeKay floats (3500 A's or B's) although the later ones (3500 C's or D's) are good floats. Likewise, I'd stay away from the early Wipline floats, though the later ones are great floats as well. The early 3730 and 3900/4000 Wip floats are just too big for a 185, in my opinion. Wip thought so as well--their later floats are much smaller.
I'd stay away from amphibious floats if there is ANY possible way to do so. Very expensive, VERY heavy, VERY little useful load, and maintenance hogs, generally speaking. Insurance???? Hold on to your hat when you get a quote for those.
Send me a PM if you want more info, and I'll send you a phone number.
MTV