1. R80.40 is the most used version and r81 already used by thousands mgmt’s and even 150 multi domains. We have solid mgmt upgrade by now and dont know of chronic issues so i am 100% sure we can help you get to R80.40 if you want to “work with us” (QA can assist).
I would personally go to R81 and even consider R81.10 on the mgmt. For Gw’s i would also go to R81 but can also see the more conservative approach to go to R80.40
R80.30 isnt bad release but it is just missing things that are already available and solid.
2. The problem why you cant delete the object is that it tells you its being used?
If so you can delete it it from “main places” like main rulebase and groups and then change its display name to “the dr gw that was removed from this mgmt” and delete sic /change the ip. This way when you look at your history and see a reference, you can see where it was and have reference - if not, you will need to delete it from all usages
Dorit