Musing on this over the last few days and I've put together a representative force to represent the King's forces at Newbury (1st). Listed as follows..
Overall Commander: King Charles the First 58 Points
King's Lifeguard (Cuirassiers) Elite, Valiant 53 Points
Byron's Horse, Gallopers 39
Aston's Horse Gallopers 39
Foote 907 Points
Sir Byron Commander of Foote 40 points
Commanded Shotte Firelocks 35 points
King's Guard
Pikemen Large, Valiant, Elite 40
2 units of Shotte 54
Charles Gerard's Regiment
Pikemen 34
2 units of Shotte 54
Sir Lewis Dyves's Regiment
Pikemen 34
2 units of Shotte 54
Earl Rivers' regiment
Pikemen 34
2 units of Shotte 54
Lord Molyneux's regiment
Pikemen 34
2 units of Shotte 54
Sir Edward Stradling's regiment
Pikemen 34
2 units of Shotte 54
Sir William Vavasour's regiment
Pikemen 34
2 units of Shotte 54
Sir Jacob Astley's regiment
Pikemen 34
2 units of Shotte 54
Colonel Henry Lunsford's regiment
Pikemen 34
2 units of Shotte 54
Sir Ralph Dutton's regiment
Pikemen 34
2 units of Shotte 54
The Horse 500 Points
Prince Rupert's Wing 343 Points
Prince Rupert of the Rhine 70 Points
Rupert's Lifeguard Gallopers, Ferocious Charge 39
Rupert's Horse Gallopers, Ferocious Charge 39
Lord Wilmots Regiment Gallopers, Ferocious Charge 39
The Queens regiment Gallopers, Ferocious Charge 39
Charles Lucas' Regiment Gallopers, Ferocious Charge 39
Northampton's Regiment Gallopers, Ferocious Charge 39
Eure's Regiment Gallopers, Ferocious Charge 39
William Vavasour's Wing 157 Points
William Vavasour 40 points
Canaervon's Regiment Gallopers 39
Prince Maurice's Regiment Gallopers 39
Morgan's Regiment Gallopers 39
The Ordnance 98 Points
Lord Percy/b] Commander of the Ordnance 40 points
Medium Gun 21 Points
Medium Gun 21 Points
Light Gun 17 Points
A total of 1695 points.
That's a fairly hefty force to go on a tabletop though! (Especially considering most games down the club have been 500 points. Perhaps it'll be for a weekend or full day's game should we ever get a venue Shall check if I have enough toys to do it. Definitely have enough infantry, unsure about the cavalry but I shall count horses tonight.
Working out from above I need the following:
5 Commanders (including the King and Rupert) which I have already, what size bases have we used down the club so far? I'll try and keep it the same
42 bases of pikemen (4 models per base(40mmx40mm)) including 10 sergeants, ensigns and commanders
60 bases of Musketeers (4 models per base (40mmx40mm))
12 bases of Firelocks (1 model per base 20mmx20mm)
72 bases of cavalry (2 models per base (50x50mm)) including 12 trumpets, standards and commanders
6 bases of Cuirassiers (2 models per base(50mmx50mm)) including 1, trumpet, standard and commander
2 medium gun bases (50 x 50mm)
1 Light Gun base (40x40mm)
works out as 420 individual infantry models, 156 Cavalry, 3 cannon and crew and 5 Commanders (+ assorted toadies for their bases) Not too much to paint

All in all a lot of metal and plastic and a smidgen of resin
This is currently sitting at 2 on my painting list, behind the blake's seven miniatures and spacecraft which need to be done for next month. Being very repetitive though, it's going to be interrupted by other projects to stop me going insane! Thoughts, opinions? Personally, I think I've got too much infantry there so if I was to drop it to 1000 points that's where they'd go from as the balance is wrong at the moment, there should be more horse than infantry (8000 vs 7000 at the original battle)