I am looking at Rampant Colonialism and Colonial Adventures as the top prospects for rules. I have a hard copy of the latter, along with its campaign supplement, on their way. I also plan on obtaining a copy of The Men Who Would Be Kings, and perhaps Flying Lead as well.
On the terrain front, my order from Crom's Anvil will be winging its way across the pond shortly.
Next steps will be to start buying figures, and pitch the multi-factional idea to my gaming compadres. My initial thoughts would be have any player who is interested choose one colonial power and also provide a unit of bad guys so that the force pool has plenty of figures from both sides to choose from.
My own purchase from Blue Moon will be the Germans and a unit of Arabs, probably Tauregs. I also want a local force, so a unit of Egyptians or Sudanese will work for the Khedive's forces. I need to really lay out a bit of the background and the various forces in more detail in a future post.