In this strategy Caste System doesn't play any role - the whole point is to recover your economy from the "shock" of the conquests. The more important classical/ancient era techs for this purpose are:
- COL, for the courthouses/Forbidden palace (as cds0528 pointed out)
- Currency, for the trade route, the ability to trade some resources for cash (remember, you now have a big area so you most probably have many resources) and, of course, Markets. Remember that you have a low science percentage, which in its turn means you have a high Gold percentage - that means Markets are awesome in this scenario (even more profitable than the libraries).
- Calendar, in many cases, to work on the (extremely profitable) Plantations.
- Sailing, in some cases, to open up better trade routes.
Of course you also go for whatever tech seems fit to your terrain, according to the circumstances. But in many cases it is much better to head for COL than, for example, going first for IW if there is no specific reason (i.e., some jungle cities). There are many variations, and each game is different; I just tried to pinpoint some general guidelines without implying that you never do anything different.
Remember that AI sucks both in specialization and city improvements. If you manage to have double the empire than the AI, there is nothing that can possibly save them (that's what I mean by "win at leisure"). After a short "catch-up period" with tech trading, you will get ahead and never look back.