Well, I'm not sure about that, but I can build siege engines with a level 5 factional MIC. About archers, I think you will have to use either mercenaries, or just foreign archers. About elephants, I suggest you use skirmishers (velites?) to lure them away and pelt them to death. It's what I used to do with my Ptolemaioi campaign when I was conquering Ethiopean lands and it worked well.