One perhaps obvious thing to watch out for is that wind can cause permanent damage to ribbon elements. Even though the R10 are sturdier than normal because have an internal windscreen to protect them, I assume (not sure!) there’s still a real risk that a stronger wind outdoors will damage the mics.
There’s plenty to choose from regarding stereo mics / mic pairs. If you don’t have a set idea of which mic technique to use and want to start on the cheap, a small matched pair of relatively low noise omnis like the Lom Uši Pro (available occasionally when Jonas makes a batch), Fel Clippy XLR (available regularly) or Naiant X-X low-noise version (available regularly but only ships to US addresses) with matching windshields, attached as AB stereo (eg. just a spaced pair), seems to be a simple but effective recipe.
Or, if you want single mic X-Y stereo, something like Rode NT4 seems to be a common relatively low-noise inexpensive choice (still about triple the price of one of the cheap lav mic pairs above though).
I have a pair of Lom Mikrouši Pro (smaller, slightly less low-noise version of the Uši Pro) with my MP6, and have been very happy so far.