Can I deploy VMware vSAN with one or two hosts initially, and later on add mode hosts?

I have two ESXi v6.7u3 hosts running independently. Want to add one or two more new hosts to my environment, but this time, I'd like to convert the environment into a cluster and take advantage of DRS and HA.

I'm familiar with other virtual SAN solutions where you traditionally have to deploy 3 hosts at a minimum to have a network RAID 5 type of protection. I have never deployed VMware's vSAN but heard people can deploy single vSAN nodes.

I'd love to hear if I can start with one or two vSAN nodes, move in some VM guests from the running hosts, once empty, it could be reconfigured (or reinstalled) and added as a vSAN node, and repeat the same procedure to add the second existing host. At the end, I would have a cluster of three or four hosts running vSAN.

Some explanation as to, if it is possible to start with one or two vSAN nodes, how the storage is configured and the level of protection, if network RAID 5 cannot be achieved at that point (can the storage protection level be changed once there are enough nodes?).

Also, there would be at the end one/two new hosts and two older hosts. They would be pretty close in processing power, memory and all would have SSD storage. In your opinion, is there a down side here for combining slightly dissimilar hosts?

Thanks,

-M