The RC51 is a great and yes fun scope to use for EAA, and for AP. Extremely sharp, flat field, with a full frame image circle. I use the APS-C sized ASI2600 with mine. I've even grown to prefer the Helical Focuser. While certainly preference for the focuser type is personal, I've found that having a ZWO EAF focus motor in-line mounted makes a more balanced, and easier to store in case setup than having the focus motor (if you use one) sticking out at a right angle. Not a critical argument or a deal breaker in any case, but just something else I enjoy about the Redcat and its helical focuser. Urban city sky glow / light pollution performance is much like any other scope, no better or no worse... I use mine fine for EAA in the city with a street lamp right in front of the house. WO's built in focus mask is very convenient.
The RC51 works with the standard ~55mm backfocus, so you can use an OAG, Filterwheel/drawer, spacers as you normally would with your ASI Cams.
Your ASI290mm mini will work fine in either the ZWO mini guidescope, any of the WO guidescopes, or an OAG. I use the ZWO OAG with the 290mm mini on the Redcat, along with a Filter Drawer with my OSC ASI2600. EAA is fantastic, and the displays always draw people at my local club's public events.