- if your plugin doesn't have a integrated arpeggiator you can buy a mini akai keyboard for few bucks. it has a builtin arpeggiator in only 2 toy-like octaves. Cheap and lightweight. I don't think it supports clock synk tho, i'll check this evening when i'm getting home.
Again, by looking at some midi controller you can find an lfo, i'm not sure which product has it.
Some effects usually achieved with lfo can be achieved manually with an expression pedal. Other effects will require a very strong foot ahahhaha
I guess they'll add those two features in a 3 version of mainstage, even tho cycling controls like lfo or arpeggiators usually implies an internal timer that can interfere with the whole performance. But request for these two features is too high to be ignored.