Planning my array Before I do anything

I want to make sure I don't rush into things, so I hope you don't mind if I pass you by my thinking before I do anything (measure twice/cut once etc)

At the moment I have an ESXI server with 6 x 8TB drives in, I am moving to a unraid server which has the capacity for 8 drives.

I want to move about 12TB data from ESXi to unraid, I am not planning to move the actual VM's as although its possible from what I've read you need twice the drive size free to do the convert. What I need to do is move the data off the "big" drives before I can use them in unraid, as such I have a 8 x 2TB drives which gives me a total capacity if 16TB (or 14TB if I use one as a parity drive) which should be more than big enough to take the data and then replace the 2TB drives one by one with the 8TB drives.

Firstly in this situation I assume its best not to have a parity drive, as A) the data "should" be on the old server so I can run the risk of not having the protection while I transfer the data, and B) by not having a parity drive it "should" be quicker as there is no extra overhead.

Secondly, to change the make up of an array pool, would it be best to leave one drive "unassigned" or even not install the drive in the first place, so I can then replace this with an 8TB when it becomes free out of the other system. I've read something that says I need to use the New Config option but this comes with scary warning messages about "reset the array disk configuration". Is there an updated guide to swapping a smaller drive for a bigger one, and would it preserve the data on the array when I do so?

TIA