Hello Asad,
SAP best practices suggests to have 2 server nodes per server. Considering your system just has 1 central instance (CI) and no App servers then you need to have 2 Server nodes, which will help in processing the messages by having proper load balancing.
In my case we have one CI and 2 app servers, hence we have 6 server nodes in total, 2 for each.
Also i would suggest you to go through the below blog to resolve the queues issue -
Queues issues in SAP PI and ECC system overview and steps to resolve it
Regards,
Nitin Deshpande