You can create VPC peering between VPCs in different regions as long as they have different ie, non-overlapping CIDR blocks. This is to ensure that the private IPAddresses are distinct.
VPC peering is the network connections between two VPC's that allow them to communicate privately (using private IPAddress) as if they were in the same network. It is a non-transitive (one to one) connection.
If you are asking about availability zones, then one. A subnet is inside an availability zone it cannot span across zones.
This can be due to various factors such as the instance type has limited resources, RDP might have connection latency or Server might have some configurations or background tasks slowing down the performance. You can used cloud watch to monitor the performance of the instance and upgrade the resources accordingly.