Hey Thermo, so needing to hit that magical 28 (not far off eh?
)
First up it is possible to make an all mounted rohan army of 28 models at 600pts, just.
If you take your three heroes and just use westfold redshields with an outrider it comes to exactly 600.
Problem is this lacks any kind of versatility.
So to get the sons of eorl and royal guards the foot troops are needed. My question about this is: How are you planning on using them?
This will define which warriors you need mounted and which you want on foot.
Personally, I like to use Rohan infantry to make a saxon (I think) shield wall. You don't have any spear support so shielding constantly with a banner behind you keeps the enemy from constantly winning fights against you.
Royal guard are good for this because of their defence and fight value.
Men of rohan are good for this because they're much cheaper than a royal guard and while they die faster (your plan for certain scenarios like recon surely?) they free up the royal guard to hit from horseback. This also means that towards the end of the game your more likely to have royal guard left alive, useful if your keeping that leader healthy.
Additionally you can equip your foot troops with throwing spears. While they are shielding in combat they can't wound the enemy but will pick up some kills before combats happen and with 8 inch range you can throw a lot of spears before engaging.
I only wish throwing spears were 1pt cheaper, as each warrior with spear is almost as much as a royal guard on foot.
Once the shield wall has locked an enemy in place the cavalry can attack the flanks, this is where the sons of eorl should (as I'm sure you well know
) be devastating.
I did a little number crunching today and came up with
Eomer, KotP, armoured horse
Erkendbrand, horse
Eowyn, armour, shield
5 Sons of Eorl
8 Westfold redshields
Rider of rohan with Banner
3 Outriders, horses
8 Warriors of Rohan with Shields
28 models, 3 Heroes, 8 Might
12 Bows
Shield wall of 9 models with a banner to help or the banner can support the cavalry as needed, have dropped Eowyn's horse on the basis that if she's leading foot troops she can hold the centre by shielding with her higher fight, or stand behind until her might has been spent then plug one of the gaps.
Kept the outriders mounted because horse archers have better LOS, the extra move keeps them in good positions to both snipe and charge, it also means with vanguard they can rapidly get to and hold objectives for you.
Kept all your son's of Eorl in but cannot find room for any royal guards, you can add some in by dropping the number of cavalry you have, perhaps to give the centre of the shield wall some extra protection or to have a small number of fearless cavalry.
I am a big fan of throwing spears but know that you aren't so much, it would be difficult to include any in this list as the pts are pretty tight.
Just my thoughts, hope this helps