The first thing I would be tempted to do would be move the pots together into clumps. This will make them easier to water when the time comes, and increase the visual effect of them. Maybe try some more pots, with some at the back raised up so you get to see everything. If you can't stretch to proper pots, try any containers you can find. You can get buckets cheap enough (often cheaper than pots), and with a few holes in the bottom, they do the job just as well. Just remember to put them to the back of your display! You can save on compost (and money, if you are buying it in) by half filling large pots with soil or even broken bricks etc. then topping up with compost.
If you're anything like me you might find it hard to remember or make time to water all those pots, so I would consider putting more stuff in the ground. Plants are generally more tolerant of neglect in the ground. If that slate is just laid on soil, then scrape the slate back and plant; if it's on a membrane, scrape back the slate, cut an X in it, and plant in that.
You can buy plants quite cheap in places like Lidl, and for me at least they often do very well. Just make sure they aren't bone dry when you buy them. And of course seeds can be a good option. Places like Lidl and Wilko are good value for those, and they often have packs of seeds for perennials which would be worth a look. Growing from seed often isn't as hard as people make out, and doesn't require any fancy equipment to get started.
If you have any friends/relatives with nice gardens, ask if you could get plants from them. Many of my plants have come from plants taken by division from friends' gardens. (With permission!)
Clear out an area of lawn and plant apple or other fruit trees.