I hav'nt any personal expierence of the trip you are intending, however I have done some of the legs in the other direction. My thoughts would be that it would be a tough sail, almost always to windward, and with a slight current against you. The Pilot charts for July for the area around Seychelles / Chagos show 70% of the wind from the S E, and around 20% from the East, with the average force of 4 - 5. These strengthen somewhat closer to Cocos Keeling ( I can definatley vouch for that). The current mostly flows West at rates of around one knot. The swell would be mostly from the S E, often with "white horses" and quite steep. The best bet, in my opinion would be to get as much Southing as you can for the mjority of the trip, as the current lessons south of 20 deg S, and so do the winds. There are variable currents close to Australia. A hard trip indeed...take plenty, plenty diesel !!!
Oh, much the same applies from June to about September.