The speedo should be fine withing 1-3 MPH as long as you plus size correctly, meaning that you get a lower profile tire with the larger wheel. The overall diameter of the combo should stay the same.
Lowering is the biggest cause of camber problems. I'm running right now dropped almost 2" and am not using any camber kits, but my camber is about .5' out of spec. No abnormal tire wear as long as I rotate them often.
Springs/shocks - how much do you want to spend?
~$900-950 will get you a nice full coilover setup. If you get springs and Koni yellows (great struts), you will end up spending
almost the same amount.