Mine is currently a WIP. Here's how I'm doing it.

I bought a box of Fireforge men on horseback, the one with half clothed horses and half regular horses. You can also just buy the horses by the sprue now. The horses I'm painting black with yellow on the inside of the capes and probably bay flesh for contrast against the yellow. I used the Titan Reaver paint scheme for my yellow, available from Tale of Painters @blogspot. (An excellent painting resource!)

The men are old metal mounted men of Minas Tirith, the kind with no shield. These were bought with no mounts from ebay fairly reasonably (they're even cheaper if they're missing their spear). They are painted the same as WoMT. Because I'm lazy and don't want to sculpt capes, I'm using the ones from the Fireforge box, fitting since the horses are all in dynamic poses. These will be painted yellow and black to match the mounts. Hoping to post pics of the finished army.

Now what are you planning to do with the rest of the Fireforge minis, you ask? Well, I've already converted them to mounted Numenorians. Simply place the head of a Numenorian on the body of a Fireforged warrior, use all the sword hands and empty shield arms in the box, add the cape and glue on a Numenorean shield. Sculpt back hair, paint accordingly and voila! A beautiful converted army!