Good lakes to learn...? Hmmmm, well, my experience is limited but I am sure others here can help, danielk. Depending on where you live there are a lot of local lakes which hold lots of fish in the 8-12" range that can be lots of fun on a fly rod. There is a report on buntzen lake in the reports section, some decent fish there. as for room to cast, you could do it there off the dock or the beach, but in the spring and summer you might be better off casting from a boat as otherwise you might hook some of the bigger fish walking around on the beach behind you...
A floating line would likely be the easier one for you to learn with, once you try that for a while, then give the sinking line a try...both have their usefullness when fishing lakes. You may also want to pick up a sink tip line for the lakes, but I am sure others will add to this...
I carry a floating, sinking and sink tip line for lakes, and a versa tip system for the rivers.
Hope that helps,
rib