450 liters is around 120 gallons. I am assuming a 4-foot tank that’s 2 foot wide and tall? A Yellow Tang would be fine, but the Regal Blue would be a problem. They get like a foot long and are powerful swimmers for tangs, I’d not put one in a tank shorter than 7-8 foot and below 200 gallons.
4 Clowns would also be a problem due to aggression. Generally it’s advised to not keep more than a pair in a tank, and only a pair of the same species.
If you want another large fish, which I feel you do, I can recommend either a One-Spot Foxface (the smallest species of Foxface) or a Marine Betta. Both get to 8”, with the Marine Betta being more cryptic and sedentary. The Regal Blue is simply not a good fit for your tank.
What species of Cardinal do you have? If it’s Pajama Cardinals I’d possibly suggest a trio. Bangaiis tends to be more aggressive towards conspecifics.
Coral Beauty works fine.
Do you plan to keep inverts? If so, you could look into some gobies and Blennies. If not, maybe a Flame Hawkfish or some other kind of Hawkfish like a Falco or Longnose? However, I would not mix a Hawkfish and a goby or Blenny in the same tank.
You could also like into basslets, all of them would be a good fit for the tank. Royal Gramma, Blackcap, Swissguard, or one of the Assessors would all be fine.
