1). If you are running OS 3.0 or above it would be the normal process, below that version I think you need to do little extra job to do, like initializing the new cluster first then bring the both clusters to the same version and then add it to the cluster. 2). Yes we can without ToR switches , we did it recently but it is a new deployment,  only need to make sure that all necessary changes been in place in the customer networking switch. I am not expert just sharing the experience, hope this helps a little bit.  
I have a customer that purchased a Powerstore 3000T and was configured as a single appliance without TOR switching.  We are now in a situation where they want to add another appliance to this system to create a cluster using a 3200T.  I have two questions -  1) Can we mix Gen1 and Gen2 appliances in the same cluster?  I believe we can, but I want to verify whether anyone has done this before. 2) Can we add the new appliance without the TOR switching by connecting directly up to the customer network?    
Powerstore Clustering without TOR Switching