I would like to know if Xposed Framework can successfully run alongside a custom rom that possesses many features or whether it has to be a stock ROM. I wasn't able to find a consensus on whether or not it was possible, so I attempted to try flashing Xposed on a Nexus 6 while running Benzo Rom (a feature rich AOSP ROM), but I was unsuccessful since I got stuck on the Google boot logo.
I don't know if there's a general rule to it. The Framework might be incompatible with some ROM, but I've never heard of such.¹ I've used it successfully on multiple devices running either "stock"² or CyanogenMod.
¹ Some modules however don't work well with specific devices/ROMs, or only with them. Examples are those written for a specific flavor (e.g. just for TouchWiz devices), or adding features from a specific custom ROM (and thus shouldn't be combined with that one).
² What is "stock"? In case of one of my devices, it is CyanogenOS. On Xiaomi devices, it's something with MIUI. On the OnePlus, it might be OxygenOS. For Samsung devices, it's something heavily modified including TouchWiz. So some ROMs (e.g. CyanogenMod/CyanogenOS) are even closer to AOSP than some "stock ROMs".
Conclusion: A generic answer is difficult. When in doubt, check for your specific combination (device & ROM) at XDA – either in the XPosed area, or in the section specific to your device.
PS: Also note that the "latest Android" is usually not (yet) supported by the Xposed framework. As of this writing, the latest supported Android version is 6.x.