Disk bad to be replaced

Hello
I currently have my Ex2 ultra with 2x6TB
Disk 2 failed and showing bad . model number : wd60efrx (pic attached)
Question:
1- i m not able to find a replacement online exact model wd60efrx
I found : WD60EFZX , can i intermix those 2 drives
What is the recommended disk to order if i consider remaining to 6TB , please share model number
2- i am thinking to upgrade to higher capacity if the price of 8TB or 10TB is close to 6tb, therefore how can i do the migration for the functioning 6tb (disk1) to the new higher capacity?
3 - is there anything to consider if i decide to upgrade to 8tb as i read better to change the power adapter from 36W to 48W (if i recall well)
4 - any suggestion for a good link to buy those HDD , i am based in UAE

All hard disks use close to the same power for a given series within some scope of < 5W.

If you get new disks get a pair of them to match each other to get the overall capacity improved.

The model disk mentioned is not the better model with 128MB cache and some larger cap disks now have 256MB