Street basis reuse the stock tophats. You will get some rear camber by lowering the car, but no way to adjust it. FlexZ has tophats with camber adjustment. A 245/40/18 is 25.7" diameter. Stock is 24.6" diameter, which is larger than a 3% difference. (which is the general rule of thumb for plus sizing - less than 3% difference) I have seen guys run that size to though. I would still get 35 series.
I lowered my car 1" and have -2.2 rear natural camber. (no adjustment) So, if you go lower you will have more, unless you have a way to adjust it.
I tried to find a answer if you will NEED lca, but it really depends on the coils you get, tire you choose, and amount you lower the car. Some guys do not need them, and some do.
Anyway, you should read through the meaty tire thread. It is THE thread for this size of wheel.
http://www.ft86club.com/forums/showthread.php?t=41083