Regrouting will improve looks to the tiled wall but grout itself is a pourus product not a sealer. The waterproofing you are talking about is probably just resilicone the shower…

Well done.
You saved yourself some money by DIY

ikea or bunnings may have a panel with a similar finish you could cut down or a drawer front the same size. Take a door off and take it with…

The doors are vinyl wrap so it will be hard to get the one small panel as they typically have a minimum order.
If it's plain white you can probably get…