Britmedic... thank you for the photo and the clarification.
I think you've done an excellent job of moiling especially for the first time around. Well-done! It is clean, crisp.
as for further useful or practical guidance I am not certain I would have any because useful guidance is only useful if it is useful to the recipient that would be willing to alter what exists. And,

you have already decided the usefulness of the space. Besides, you are the Author of the garden, not I.
As a result I only have my preferred experiences and observations to offer, such as:
- you have an awful lot of space, enough for a teahouse with an inner and outer roji with machiai. For Japan that is a large space.
- there certainly is beauty in contrast, though a tea garden, for me, is about harmony; the walk through the forest to the hermitage, rather than contrast (in my opinion)
this is of course what conversations are made of, wherein there is neither winning nor losing, right nor wrong, as the ideologic beauty in each garden only becomes clearer and refines over time through use and maintenance.
As with most gardens, one needs to live with them for a while to figure out what to tweak next as well as how to manage it.
Perhaps what could be suggested is to research a bit into the placement of the ladle that you have on the tetsubachi.
very interesting... and I suspect that George would be a better judge of British Japanese gardens than I as the evolution and placements presented, came to rest differently in the UK through their World Expositions, than in the rest of the worlds Expositions.
p.s. what would the 'zen' part of the garden be? is there an Zen idea that goes with this garden? edzard