It's very similar to what I'm working my Rohan force up to, trying to get enough for Theoden's Battlehost. That 4+ Earth Shattering charge is amazing, and Royal Knights are very tough for a cavalry unit. But that's a LOT of metal figures
(unless you are being allowed to proxy RoR). I'm starting with one company of Royal Knights and the rest RoR going to Erkenbrand's Riders (strike as Monsters to get around that pesky Legolas or other Cav)Rohan has some nice Epics, even though some would see a lack of ES Heroes a serious drawback. I think it matters, but maybe not too bad as your base fight values are ok.
I would consider dropping some of the Heroes (especially your un-allocated 90points and Merry) in favor of some RoR to operate in 2-3 Company harassment forces. You want to keep other Formations from interfering with your main hitters, maybe tie units up or get in a Flank/Rear to weaken their return strike. I understand the benefit Epic Sacrifice could give but that's a lot of points you are investing in basically sacrificial models.
Your core Formation with Theoden will be your major thrusting force as you know. Theoden gives the whole Formation his Fight and if he calls an Epic Charge (free with Touched by Destiny
) then they are F7. Against Infantry this higher Fight, plus Cav charge bonus, will mean you're throwing a LOT of dice, and you're S4 with +1 lances. You already have a good Defense but if you have Theoden call Epic Defense (I'm pretty sure he has it) then you are now a very survivable D7(8)...and he may even get his Might back if the dice treat you fair. Unless they are hitting you back as Cav you could do a lot of damage with this and with a low Earth Shattering Charge target now you will probably hit them a second time. 
Another option would be to free up some of the points in your current Heroes to pull in Gandalf the Gray. He also has Epic Defense (and Touched By Destiny) so every turn they are alive you can get a free +2 Defense and +2 Fight (if you charge). He can also use his special spell to guarantee the enemy is at F0 when you hit them. With Theoden's special rules this means all the Cav in his Formation would hit Infantry with 15 dice per company, at S4 +1 lance and with an Earth Shattering Charge on 4+. You may wipe out a major Formation in one turn if you can set it up well. Theodred can duplicate another's Epic Action similar to Gothmog so if someone calls Epic Strike on you then you can counter.
Typical threats are easy to spot: Running into Khamul's formation would probably be a very bad thing as the bouncebacks will likely wipe you out faster than his force so he's the biggest to avoid. But as for any other Formation with some Epic Strike models in it just use your Royal Knights. No Hero so noone to ES against.
They still benefit from the 4+ Earth Shattering charge and if you have Gandalf in the Royal Guard blast them down to F0 in advance (yeah, they could Will of Iron but that's still a Might burn they may not think of in time) then Royal Guard would still be rolling 10+ dice per company that hits and then 50% likely to do it again while your Royal Guard stays slightly back to avoid an ES risk to your key Heroes.Other weak points exist and WILL be exploited so you want to play test the force as much as possible in advance. I was slaughtered with my first several games with my Wood Elves until I learned how to play them better and now they serve me well. I'm going to get slaughtered when I start to play Rohan as well.
