So after getting decisively defeated several times, it's obvious I need more practice. And I don't know anyone at my level of experience or ability who has an army I can borrow.
Therefore, the best plan is to go ahead and buy one. But my eyesight is so bad painting isn't very enjoyable.
So I've calculated it out, and I think I can afford a British and OPFOR French Peninsula army from https://www.stonewallfigures.co.uk/product-category/painted-battalion-packs from Stonewall Figures.
I've got one brigade of light infantry from them, and I think the remaining Anglo-Portuguese army would be about $400 Australian, and the French OPFOR about $500-600. I'd want to give them a wash and still need to base them, but I think thats the way to go.