How to restore WhatsApp messages on new iPhone

Hi guys - i wonder if you can help me.

Firstly, apologies if this is unclear or a little wordy but here goes.

Yesterday, I was setting up my new iPhone 12 - everything worked as expected and my old phone was copied in it’s entirety through the usual setup process. However, I had decided to continue using my old iPhone until I receive a case (I work somewhere where it’s very likely my phone will be thrown around…). I went back onto my old phone and reactivated whatsapp on there. However when i did so, and restored from a backup, it was missing message history for the past 6 months.

Upon investigation, for whatever reason i had turned off WhatsApp chat backup so this is my fault - not anyone else!

I’ve done some searching and form what I gather, if the WhatsApp backup isn’t sufficient, then I can attempt to restore my phone using an iCloud backup or alternatively, using some sort of recovery software.

I actually played around with some recovery software last night and all I could find was data from the previous backup (May 2020). 

Therefore - I think m only option is going to be going through iCloud. Couple of questions here;

1. Will an iCloud backup (I’ve checked and WhatsApp was set to backup to iCloud) offer anything different to the backup held on whatsapp (it says that the last one was done on Saturday night). Ie will it give me all messages as of and up to Saturday, or will it just be the same as if I attempt to restore the backup on Whatsapp?
2. I’m not incredibly tech savvy and I understand that I have to Erase all data first - I’d just like some advice on whether or not my iCloud backup will be sufficient when restoring (ie it will go back to exactly how it was on Saturday night when the backup were done)
3. Instagram is also not set to backup to iCloud. When i go to erase all data, i have a warning flag saying that any data that isn’t backed up (specifically calling out Insta and 3 other apps that I’m not bothered about) will be permanently deleted - what exactly is it that will be permanently deleted? Want to confirm that it won’t be my actual instagram account and content within it?

Thank you so much! Really appreciate any help or advice you ca give.

[Re-Titled by Moderator]