I pretty much did same as everybody else, went east with first settler to try to block off Mansa expansion. He had 6 cities ... at his peak

... but I don't know how many he had at 500ad. In any case he only got one city site west of Timbuktu, immediately to SW (Djenne, at the top of that inlet bay), I moved quickly and got the north coast site opposite it, giving me a home base for striking at Timbuktu first when the right moment came. I find it hard to imagine limiting only to cities total; in my game he ultimately founded four cities EAST of Timbuktu, plus Timbuktu itself, and finally Djenne. Did those who kept him to 3-4 cities settle some cities east of Timbuktu too ?!?
Anyway I boxed him in as best as
I thought possible & watched him focus on religions (Hinduism & Judaism both in Timbuktu; I immediately put a "Wall Street" note on that city

) & then when I got open borders with him, watched him send missionaries my way. Figured I'd just site back and let him do that, and trade tech with him for as long as he could keep up with me. All-in-all I found this game had a fairly obvious strategy: settle in place, explore with warrior to discover island setting, block off MM expansion & trade with him, go for key wonders like Oracle, AP, Pyramids (missed that one to some off-island civ), and GL (MM beat me to that, with his marble). Seems like all no-brainers (but I wait to read what the really clever strategy was that I didn't think of).
The no-brainers here included the capital site, for me. Before starting I read the pregame thread quickly, and marveled at the talk of how the starting position was not very good. Then I went and started the game and settled in spot. Seriously, I never got what the fuss was there, sure there were not any immediate resources, and no sea, but MAN with all those flood plains and rivers, did that city turn into a kick-arse bureaucratic capital once I got Oxford & later Dikes in there. I mean how many tiles were river, something like all but 3-4??? Financial trait seemed to dictate yet another no-brainer, I cottaged every single non-resource square (getting 3 coins per cottage right away for most), except that I left the two plains on the SE edge of FC with forest, as a half negation of the yuck faces I was getting from flood plains everywhere else. This is a monster Oxford+capital site, I'm flummoxed why some kvetched about it. I did think a little about moving one square to settle on the banana and get one extra food right away, but in the end decided it wasn't worth losing those flood plains.
I don't remember exactly where I was at 500AD, but probably either at war with Mansa Musa by then, once he had outlived his usefulness as trading partner & finished my shrines for me in Timbuktu

, to take the entire island for myself (and the mouth-watering Timbuktu especially), or preparing else for it. Not much else to say, except that I got Oracle (recall I got CS for it) and also got AP (always a priority in my BTS games). As a consequence of pushing for CS sling and AP I got both Confucianism and Christianity, plus MM got Islam, so there were 5 religions founded on our little island ... probably bad omen for diplomacy later!