Some greenhouse questions

Welcome to the forum @LettuceG

You do have some unusual issues there. My garden is on a hillside and pretty windy, I have had some problems with high winds and glass panes blown out of my greenhouse - very rarely maybe twice in 10 years. I replaced one pane with an acrylic sheet and this pane regularly blows out so really I should have glass when I get round to it.

Your choice of toughened glass sounds wise.

When the wind whips over a greenhouse it creates uplift like an aeroplane wing and can lift them up and away. My greenhouse has a steel base which is fastened into the ground with long metal spikes, yours would need screwing securely to the decking, but what is holding the decking down, presumably just gravity? You may have to consider a way of anchoring the lot down.

I am unsure about the moisture aspect, presumably you will grow in pots and/containers. These could be on big saucers to catch any overflow but there is obviously risk of seepage into the wood. It depends on what you grow on how humid you want your ghouse. You could have a moisture barrier such a UV stabilised plastic sheet and provided there was ventilation under the decking that might be OK.