The taxonomy of concepts and terms is very complicated, and the documentation is still pretty sparse.

1. For creating and working with kubernetes, 
why there is a variation like single node and master in same or in VMs? 
Why there is a deviation in cluster container?

The deviation is to support many distinct use cases- container workload developers working on their laptops needing what amounts to a fake cluster without a lot of operational ceremony; kubernetes ops folks learning and testing on a small but real clusters; and real production workloads for varyingly-sized plants.

For the first case, for container workload development, there is a piece of software called minikube, which is like a distribution of kubernetes that automates creating a single virtual machine- using VirtualBox or other desktop-class virtual machine tooling- that is preconfigured to run a combined kubernetes master and node, sufficient to be able to run real kubernetes workloads, but on a laptop.

For the second case, for non production purposes, the master and worker functions can be run on a single machine, or a single master machine can be used with a small number of worker machines.

A production kubernetes cluster will usually have 3 or 5 or 7 master machines- VMs or bare metals. Multiple masters are needed to maintain quorum for etcd- where kubernetes stores all runtime state- in the case of machine failures. 3 master machines allow for 1 master machine to fail without disrupting the cluster. 5 masters will tolerate 2 master machine failures, etc.

This number of masters can support a large number of worker machines- dozens to hundreds- running the container workloads. In a production environment, one would not want to run client workloads on master machines.

2. How I can decide whether I need to choose single node and master 
in same machine. Or do I need to use Vms for different nodes?

See above- for development, use minikube. For production, plan to use multiple redundant masters if you are running the cluster yourself, or use a cloud provider's managed kubernetes offering.

3. How the Minikube and Kubespray is providing different methodology
in kubernetes architecture?

Minikube is for development only. Kubespray is one of many tools that provides some automation help when building a production cluster. Kubespray's distinguishing feature is the use of Ansible for machine setup and automation. This may or may not be desirable, depending on your comfort and interest in Ansible and/or its competitors.

4. Why have so many options when kubernetes is the product of a 
single source - google.

Kubernetes certainly originated in Google, but now there are hundreds or more engineers across many companies, including Microsoft, Amazon, RedHat, Oracle, and tons of tiny companies, actively working on it. It is a remarkable project.

5. If I am installing kubeadm, kubernetes-cni and kubelet in my ubuntu 16.04
Can I initiate nodes in the same machine ?

Kubeadm is a setup tool, not a production runtime tool, but yes, you can run containers on the same machine as the bits that are needed for a kubernetes master. In addition to etcd, kubelet, apiserver, controller manager, you need to run Docker as well- Kubelet talks to Docker to schedule containers. I would only advise NOT running anything else on this machine- improper configuration can cause problems with the machine serving as master/worker so any other work will be lost.