Please Answer

Dear folks
I am British national and exercising my treaty rights here in ireland .
my husband received his Stamp 4 EUFAM recently . We have couple of question . Can anyone advise us what to do ?

1 ( My hubby travelling to Pakistan next month in October and he got Temporary Stamp 4 IRP which is valid until Feb 2020
what if he dont get my stamp 4 EUFAM RC before October is there any serious issue coming back to IRELAND with his Temporary Stamp 4 IRP because its take a lot of time to get appointment with immigration officer outside of Dublin as immigration officer is not very good and unprofessional where we lives at the moment .

2 ( What if i change my job near in future or we change our address will we suppose to inform INIS immediately at this stage ?

3 ( Can my hubby travel to the Uk to visit with me on Stamp4 EUFAM however he did overstay on his visa back in Uk will there be any issues ?

Please help
Many thanks
Regards