Wiring a new shop

Ok. Here is the scenario I am putting a 200 amp main breaker panel in this shop which isn’t gonna have much for power few 120 outlets one welder outlet and two 50 amp rv outlets some light and garage door. Ok first he had the meter socket switched to a double throw for a generator. There is no room to double lug on the meter socket so I have have to use the lugs in the panel so what I am wondering can he run his house panel and a 200 amp panel for his shop. Under a 200 amp main I will try to attach some pics. And the. What wire do I need if I am going under the 200 main I need 4 wires right? Or can I use 3 wire like 4/0,4/0,2/0 then for grounding and bonding he has a cee but do I still need building steel as well —— I suppose it depends on the wire right? Thanks all.