1. The VPC network and the VPC subnets.
2. A way to determine the network address – in CIDR, IP addresses are described as consisting of two groups of bits in the address: the network address and the host address. 
3. Between /16 and /28.
4. Public subnets have a route to the IGW while private subnets don't.
5. IGW for public subnets, NAT gateways for private subnets, VPN and Direct Connect for on-premises.
6. By default, transient traffic isn't supported with VPC peering. To achieve this, a proxy instance could be installed in VPC B, and traffic for VPC C from VPC A would be redirected to the proxy.
7. You didn't allow the ephemeral ports on the outbound policy of the NACL. NACLs are stateless and the return traffic needs to be allowed. Determine the ephemeral ports the instance responds on and allow those in the NACL.