That is awesome. You have to quit thinking about going back and forth. Sure, I think you want to know if you can go back to the other network, but don't worry about the steps. As Sandeep says, you are either on the domain or on the workgroup. My computers have been on the domain for years. Occasionally, I remove one and reattach it to fix it. You are changing it exactly the way I wrote. It is cumbersome, because you are not meant to do it. By the way, when you attach the same computer back to the server, you should change the name such as amazing to amazing1. Not good to install over the other user.
You can't connect the other ACs because they are on the workgroup. Different networks. Computers have to be on the same network to connect. You can see them, just can't connect.
As far as SSDs, I am in the same boat. Tough question. But, in my opinion, I would go with 256GB if you are going that way. You ALWAYS do RAID.
Will it speed things up? It will pretty much speed everything up. I see Sandeep is typing faster than I am.