Some issues with the Spanish side is that nobody makes (in 40mm) , Grenadiers, Cavalry, firing/skirmishing Infantry, Infantry in civilian dress, Artillery.

So quite a task to recreate.

The solution is to create a representative selection of regiments. 1st Division (Cagigal) looks the most promising, there is a mix of 1802 and 1805 uniforms, Light Infantry (Barbastro), Infantry in British uniforms(Buenos Aires), but with the clear issue of the Grenadiers and Artillery figures.

Spanish OOB.

Army of Galicia - Blake

Vanguard - Maceda
Infantry
Zaragoza - 1 Bn 700
2nd Light of Catalonia 1/2 Bn 400
Light of Gerona 1/2 Bn 400
Grenadiers 2Bns 300 (Grenadier Companies of Zaragoza, Mallorca, Aragon and Vol de la Corona)

Cavalry
De Montesa 1 Sqn 80
Dragoons de la Reina 1/2 Sqn 70

6 Guns

1st Division - Cagigal
Rey 2Bns 700
Mallorca 1Bn 1000
Hibernia 2Bns 1200
Buenos Aires 1 Bn 500
Light of Barbastro 1/2 Bn 550
Provincial Grenadiers 2Bns 900
Militia de Salamanca 1 Bn 266
Militia de Tuy 1 Bn 580

5 Guns

4th Division - Portago
Grenadiers 2Bns 300 (Grenadier Companies of Toledo, Navarra, Sevilla, Napoli)
Principe 2Bns 1600
Toledo 2Bns 1400
Aragon 1 Bn 1068
Militia de Santiago 1 Bn 800
Militia de Lugo - 1 Bn 500

5 Guns

HQ Guard
Voluntarios de Navarra 1 Bn 754
 4 Guns

Army of Castille - Cuesta

1 Division
Covadonga 2 Bns 1500
1 Tercio de Leon 1 Bn 800
2 Tercio de Leon 1 Bn 800

Cavalry
Guardia de Corps 1 Sqn 100
Carabineros Reales 1 Sqn 160

2nd Division
3 Tercio de Leon 1 Bn 800
Tercio de Alba de Tormes 1 Bn 600
Tercio de Valladolid 1 Bn 700
Tercio de Benevente 1 Bn 800

Cavalry
de la Reina 2 Sqns 300

As I have said before, to do all of these would need a sizeable chunk of funding, which I don't have!

Clearly, to do all of the units involved at Medina de Rio Seco would involve a substantial lottery win and a very big room to game it in. Neither of these is applicable at the moment, so I'll have to make do with creating a representative selection of troops.

My interpretation of the OOB for Medina is as follows (I've gone mostly with the Partridge and Oliver version). I have also commented on the availability of figures.

Part 1 - The French

Imperial Guard - nobody makes any of these in 40mm!
Fusilier Chasseurs - 2Battalions
Fusilier Grenadiers - 2 Battalions

1 Squadron each of
Chasseurs
Chevau-legers
Dragoons
Gendarmes (Oliver and Partridge suggest that the Guard Cavalry was only Gendarmes)

10 Guns

Merle's Division
47 Line - 2 Battalions (some sources suggest 1 Battalion)
2/3rd Swiss - 1 Battalion
14 Provisional Line - 1 Battalion
86 Line - 2 elite companies
13 Provisional Line - 4 Battalions
17 Provisional Line - 4 Battalions
18 Provisional Line - 1 Battalion

12 Guns

Mouton's Division
4 Leger - 3 Battalions (Leger not made in 40mm)
15 Line - 2 Battalions

6 Guns

Lasalle's Brigade (nobody makes a Lasalle figure in 40mm, which is a shame)
10 Chasseurs a Cheval
22 Chasseurs a Cheval

So some real issues here. Nobody makes the Guard at all in 40mm (Sash and Saber does Guard Grenadiers a Cheval, which could double up as Gendarmes at a pinch).

Nobody makes figures for Leger in 40mm, which could be just a paint job to make do, but I would rather have specific figures, there are some uniform differences from the Line.

A Lasalle personality figure would be great, as would a Bessieres.

The question is, how to get around the lack of availability of some key troop types.