Are their any tribal Muslim states? A Muslim merchant republic seems powerful, getting both the easy Muslim CB's and Merchant republic advantages.
If not, just take a tribal pagan and convert to Islam, then change to a merchant republic.
That and the more wives = more kids = more trading posts
But I'd suggest not bothering for a while because CM tribal->merchant republic is hideously glitched, CTDs as soon as you try it or, if you have 2.2.01, no patrician families
Nope.
What about the Persian coast then? I'm trying to find a way to create a Buddhist Republic.
Can tribal Christians take concubines and convert via pillow talk? I could start in tribal Abyssinia, go sack the Buddhist coast by boat and take a Buddhist concubine.
If this doesn't work I guess I could do it with the Norse too... Start in 867, reform, reach Egypt through successive prepared Invasions, put some boats in the Indian Ocean and go raid the Buddhists.
Bummer.
Anyway here's the plan:
I'll start in Sweden and as soon as the Viking Age begins I'll invade Khazaria or Hungary, carve myself a Norse kingdom in that area and move my capital to Crimea. From there I should be able to reach either Egypt or a Muslim nation with holdings in the Persian coast via the navigable rivers. Then all I have to do is raid Lanka or Bengal until persuade a nice Buddhist gal to come back with me. Then I'll create my Norse Buddhist republic of Crimea, educate all my heirs in Learning, spam Universities and see how long it takes for me to outshine everyone in tech while I try to de jure drift the entire Black Sea coast into my realm.
Sounds like a fun playthrough.