I am getting into wet plate myself and although my ultimate goal is to be able to shoot 11x14, I agree with the idea of starting small. I am building a custom holder to work with an 8x10 camera that will allow me to shoot 4x5, 1/2 plate and whole plate. I have a couple of more modern lenses that are fast enough to shoot with and for the time being I will make ambro negatives in 4x5 that will allow me to do enlargements up to 11x14. With whole plate images I will experiment printing with plt/pld, albumen and Azo.
Eventually I hope to fnd an appropriate lens to cover 11x14, then I will build a camera around that. I have a 355 G Claron but it is probably a little slow for portraits.
And as others have pointed out if you plan on shooting in the field you need a darkbox. I figure that once I get a workflow established working with smaller plates I can scale up a darkbox and silver bath for 11x14.
But initially I will stick with 4x5 plates as I learn more about exposure, and the in and outs of the chemistry. Much less expensive making mistakes with smaller plates unitll I get the feel for everything.