Basically, yes.
However don't expect to get it perfect first time, its a very time consuming process.
Also I'd recommend you caulk all your brushes before you go any further.
i've created the patches, though when i select them all , edit the vectors, etc, moving the edge vector of a patch only moves that patch.. thats meant to happen right? if so, i see what you mean by it being hard.. i mean, really f*cking hard. i really cant see how you managed that map! i'll give it a go.
would it be possible to make a really simple base patch, and then create hills or whatever by overlapping other patches?