Cardinals aren't much bigger, especially the males but they are more likely to require soft water, they're hard to find for sale in hard water.
I think the minimal look of the tank is very good and if you're happy that's even better, but in my view £200 seems rather steep - regardless of the brand. I'd of gone for something like a Fluval Roma 90 and probably still had some money left over - even with the cabinet. Although if you like it and it fits with your home that's great. I just prefer more natural looking tanks but that's me. As I said though, the way you've set up your is great, you've made excellent use of the available space.
Well Done and hope you enjoy your tank when it is stocked,
AmazonFTW