Hi,
I only play with RA mod, and in beta version, you could play more unit. You can't play spanish or french unit, but on UK side, you've got the Trafalgar class playable. A new version of RA (Reinforced Alert) mod will be out in a few (I hope
) with I think new units.
You can search also in this forum for LWAMI mod and Alpha Tau. But as I don't use them I can't tell you.
You can also try to mod the playable unit. I'm trying to replace the Trafalgar by a Rubis class...