Your severum are unsexable at that size, and will be too big for a 200l soon, in how I would keep them. Adding a Uara to a tank that size?
Yikes.
It's never a good idea to go with a "they" who then takes your money. The supposed expert may be sincere and just badly trained in fishkeeping,or they may have a 'sell fast and let them die young' approach to fish.
Years ago when I was new at Cichlids, a clerk refused to sell me a fish because he said I was overstocked. I wasn't very happy with him, but I said nothing. I went home, thought about it, and went back to thank him. I was met by a smiling guy who told I could add several of the fish to my tank. I asked where the original guy was and was told Mr Smiles had replaced him. He hoped the other guy hadn't been unhelpful in selling fish.
That store lost a customer, and I learned a little more about retail.