When I start adding onto the starter set, such as adding turnoffs, other items. Will I need a new controller? I notice the standard speed controller has only two accessory terminals. Suggestions are appreciated.
Depending on how large of a layout you intend to build, the standard controller should be sufficient.
I'm not aware of any controllers that have multiple accessory terminals, but if you need more connections you can use terminal blocks.
the switch control boxes should be designed so they gang together. a single cable from the accessory terminals on the controller to the boxes will power them all. You are only going to be throwing one switch at a time so it doesn't matter how many boxes are in the string.