UCS file migration on differing OS versions

We are currently upgrading the F5 load balancers of our customer, from iSeries, to rSeries.

old F5 load balancers:

• model: BIG-IP i5600 (C119)
• OS: 12.1.x (either 12.1.2 Hotfix HF2 2.0.276 or 12.1.4 Final 0.0.8)
• GTM / DNS configurations: enabled

new F5 load balancers:

• model: rSeries (2600 and 4800)
• OS: 17.5.1.6
• GTM / DNS configurations: no longer needed, as per our customer

questions:

1. Noting the OS versions of the old and new F5 load balancers...

Is this the ideal OS upgrade sequence? (based on F5 K13845)

BIG-IP 12.x > BIG-IP 14.x > BIG-IP 15.x or BIG-IP 16.x > BIG-IP 17.x

2. BIG-IP 14.x is no longer available in F5's Downloads website.

Are there any other methods for obtaining a copy of BIG-IP 14.x?

3. About UCS file migration, from old to new F5 load balancers:

Would there be any risks, configuration-wise, if we do the following steps?

- we take the UCS file from the old F5 load balancer, which is running on BIG-IP 12.x

- we import and load that UCS file onto the new lab F5 load balancer, which is running on BIG-IP 17.x

4. Since our customer advised that they will no longer need any GTM / DNS configurations on their new F5 load balancer:

Should we delete the bigip_gtm.conf file from the contents of the UCS file of the old F5 load balancer, before migrating to the new F5 load balancer?