Your apparently simple question is affected by which set of aviation rules your "operation" has to operate in.
In helicopters weight/mass is critical. A multi-role helicopter has to carry equipment for all roles which reduces the available mass for other things. If a set of aviation rules is then imposed which requires OEI hover capability (for example) it significantly reduces the ability of the aircraft to operate. The other important mass is the max fuel that can be carried.
Why did you pick an EC145? Although the EC145 is presented as a new generation aircraft in certification terms it is a BK117. The BK117 is an older aircraft and does not perform as well as other modern helicopters OEI or indeed when heavy.
You probably need to reveal a bit more of your "operation" to enable us to help you.