The first question to ask yourself is what kind of triggering system do you plan to use?
All the Yongnuo flashes with "EX" in their name can be used as a CLS slave.
Dumb optical (S1/S2/SU-4)
If you want to use dumb optical triggering, then all the current Yongnuo flashes have S1 and S2 "dumb" optical slave modes in them. S1 fires on the first flash it sees, S2 ignores the first preflash.
manual radio triggers
If you want to use manual radio triggers, then all of them should work.
TTL radio triggers
If you want to use TTL radio triggers, then you want to stick with the TTL Yongnuo models that don't end in zero (+ the YN-500EX) and that have all the pins on the foot (i.e., avoid the YN-560EX/YN-EX600 and YN-510EX which are TTL-capable as a CLS slave, but only has the sync pin on the foot, so won't be TTL-capable on a flash hotshoe or a TTL radio trigger like the YN-622N).
Notes on Yongnuo's trigger incompatibilties
Yongnuo's two types of triggers for Nikon are incompatible with each other.
There are the RF-602/603/603II/605 triggers, which are manual-only. They can only communicate the sync (fire) signal from the camera to the flash. None of these triggers communicate power control. And the 602 triggers do not work in concert with the others. The YN-560-TX dedicated transmitter can be used in concert with these, but only in either 602 or 603-compatibility modes (so you can't mix 602s in with the others), and can control the power/zoom on the YN-560III/IV and YN-658 flashes--but only on these three models. If you need to add any other flashes, you must add an external trigger to act as a receiver, you will have to set the power on the flash directly, and the only thing you can do is fire the flashes in sync.
If you get the TTL-capable YN-622N triggers, and use the YN-622N-TX dedicated transmitter on camera, you'll have full i-TTL, HSS/FP, groups, and zoom control over iTTL-capable flashes (Nikon, Metz, Nissin, Sigma, Yongnuo, etc. etc.). But a manual-only flash can only be fired manually, and there will be no remote power control, because power control is done via the hotshoe communication the manual flash can't speak because it only has the one pin.
You can get the 622 and 560 triggering systems to work together, but it requires either stacking a 602/603/etc. transmitter on top of an on-camera YN-622N, or using a YN-560-TX to control a YN-622-TX, which is not the wished-for behavior. The 622 triggers cannot directly fire the manual triggers and vice versa.
Obviously, you don't have to stick with Yongnuo triggers or Yongnuo flashes for compatibility along these lines. There are speedlights that are CLS and iTTL compatible from a variety of manufacturers that are compatible with Nikon's own CLS/iTTL-capable speedlights (SB-600/700/800/900/910). Metz, Nissin, Sigma, Phottix, Yongnuo and many others make CLS/iTTL compatible flashes as a variety of pricepoints, feature sets, and reliability.
And if you just want manual triggering, then the possibilities widen even farther, because single-pin manual-only flashes are much easier to build. And again, you can find models across a spectrum of prices and robustness/features from makers like LumoPro and Phottix.
Triggers, likewise have a variety of pricepoints and capabilities and robustness, and there are systems that have manual and TTL triggers that, unlike Yongnuo's, are compatible. PocketWizard, Radiopopper, and Phottix all make TTL and manual triggers that work together.
One more thing to keep in mind: speedlights are at the low end of strobe lighting when it comes to light/power. If you regularly need to light large groups of people or to balance against bright noonday sun they will not be sufficient to the task unless ganged up with multiple units, and you may want to consider barebulb flashes or studio strobes instead. Speedlights are for going small and light.