The long and the short of it is that none of the sources I have looked at so far really agree. There are some units whose strength and location on the battlefield are known - like Rupert and Maurice's Lifeguards, or the King's Lifeguard of Foot. So far however, I am coming up with strengths which vary greatly. from 3300 to 5000 foot on the one hand and 4100 as many as 5000 horse.
Currently I am strongly tempted to split the difference at the lower end and guesstimate 3500 foot and 4500 horse. Note that this is a ratio of 7:9.
I am perfectly happy to be corrected in any of this; my reading has not been comprehensive.
Translating this to the table, and keeping in mind that I think I'd like to keep this within a 4' frontage so as to allow me to represent the Sulby hedges on the Royalist Right, I'm thinking of a maximum army size for the Royalists something like 164 foot and about 200 horse. Not perfectly at that ratio, but not too far out.
I'd break the foot down into four, thirty-two* figure units and one forty figure unit. Two of the thirty-two figure units would each form the first and second lines, whilst the forty figure unit would form the reserve.
The Cavalry I would like to see in two lines, each of five units of eight figures per wing. Of the remaining forty figures, twenty-four would be stationed behind the Second infantry line, whilst the remaining two units would be with the reserve.
This is not perfect, and again, I am more than willing to be debated on this deployment. Certainly I would like to have less cavalry!
*16 muskets and 16 pike