I bought those exact wheels about 5 years ago to replace my old steel Le Tour rims which were getting a little too dinged and bent up. I paid about $80 for the pair from my LBS. They've served me very well with at least a couple thousand miles so far. I move them from bike to bike, depending on what kind of terrain I'm tackling (they've got my widest tires on them.)

Apart from the fact that you'll stop a lot better, they are somewhat lighter and definitely stronger, being double-walled.

Now to the freewheel. You're going to need a special tool to swap your old freewheel over. Maybe the guy you're buying the wheels from has one and will help you with that? If he's got a lot of bikes he probably does. Or you might consider shopping for a new freewheel with a larger big cog on on it, if hills are a concern. I've had very good luck on this with most of my bikes. Tons of decent cheap freewheels on eBay, and if you post a picture of your rear derailleur, we can give you a ballpark figure of how big a cog can fit under it. (There's a huge difference climbing hills between a 24-tooth cog and a 30.