You may want to consider buying a modified PMD620 from Oade Brothers if you're going to be recording ambient nature sounds and quieter concerts, the stock unit is pretty noisy. Otherwise you'll probably need to run an external preamp to get good results for those applications.
And yes, your choice of mics will depend on what you want to do with them. If you're looking for something small and inexpensive and suitable for stereo music recording, I've been very happy with the results using my Church CA-11 cardioids with the PMD620.
I seriously considered going the Oade Brothers route, but three things prevented me from going forward. First, I live in Canada and Oade Brothers will not ship outside the US. Second, there's the exchange rate issue. At current rates, buying a PMD620 from any US retailer will cost roughly 1.5X (after shipping and taxes at the border are applied) what I could buy it for in Canada with taxes/shipping in.
Third, Oade only offers a 90-day warranty on the mods. Marantz will not honour the factory warranty on any units that have been modified, to say nothing of the fact that the warranty is already toast the minute the product is shipped outside the US, again the result of Marantz' warranty policies.
Church Audio mics look like an interesting alternative. Chris (the proprietor of Church Audio) is located within a four-hour drive of my city, so shipping would be super quick and there'd be no exchange issues to contend with.