Verify session size on the server

The following method is used in a web form application to save logged-in user information:

public Usuario UsuarioLogado
{
    get
    {
        if (Session["Usuario"] != null)
            return (Usuario)Session["Usuario"];
        else
            return null;
    }
    set
    {
        Session["Usuario"] = value;
    }
}

In case I use a class because it will save various information that will be used in various parts of the application.

What is the best way to create Sessions ?

Using the class? What care should be taken in this approach?

Or Creating multiple% of individual%?

Session["ForcaTrocarSenha"] = usuario.FirstOrDefault().bit_altera_senha;
Session["SenhaAtual"] = usuario.FirstOrDefault().txt_senha.ToString();
Session["Login"] = usuario.FirstOrDefault().txt_login.ToString();
Session["IdUsuario"] = usuario.FirstOrDefault().int_id_usuario.ToString();

In my understanding, excessive use of Sessions will overwhelm server memory!

How can I check the memory consumption of the Sessions of an application on the server?

Would you like to do this via a web application form?