AOS/Aruba upgrade pitfalls?

Part of the 'we're upgrading everything' post. This time it's the wireless controller. Going from a 4700 to a 7210 from aos 6.4 to 6.5 and as far as APs it's 125-ish to 315s. I'm decent doing admin work and installing APs, but this is my first time doing a controller hardware replacement.

So my questions:

Can I import the config from the older box to the new one (with some tweaks)? We'll probably stagger the install since we won't be able to replace the APs fast enough. So old and new would have to work/overlap for a while until all the old APs are gone.

I saw a 'zero touch' feature on the quick install guide. Is that something I can use in this scenario?

We're installing 2x 7210s and about 300 APs. I know they can handle 512 APs. Do I set it up as master/slave or as one logical unit?

Any other pitfalls, checks, new features, etc. I need to look into while we're at it?