Transferring data to a different Apple account

This is possible with caveats.

Due to the limitations of ASC in limiting the length of this reply, I'll have to split this explanation into two parts.

Part One

To summarise your perceived intent...

1) You wish to copy/transfer all data from an existing to new iPad.

2) You intend to use the new iPad with a different AppleID to that used with the original iPad.

This is possible, but the process needs some care - as otherwise, sensitive data (e.g., account passwords, Calendars, Contacts etc.) that you might not wish to transfer will be merged between AppleIDs.

Done right, no data will be lost from the old device; if the worst were to happen, you can always start again. As a precaution, it is always wise to begin by ensuring that you have either a current iCloud or iTunes backup of your iPad:

How to back up your iPhone, iPad, and iPod touch - Apple Support

Next, begin by transferring all data and settings from the old (source) to new (target) iPad - initially using the AppleID used by the source (old) iPad.

Transfer

These support pages should get you started with setup of your new iPad - and the methods of transferring your data from old to new iPad:

Set up your iPhone, iPad or iPod touch – Apple Support

Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support

Use Quick Start to transfer data to a new iPhone, iPad or iPod touch – Apple Support

If the donor iPad, from which you are transferring your data precedes iOS12.4, QuickStart will not be available.

“Transfer” is rather a misnomer. In reality, your data and setup is merely cloned to the new device. Nothing is moved or removed from the original device.

An alternative is to restore either an iCloud or iTunes backup to the new device:

How to back up your iPhone, iPad and iPod touch – Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

NB: Apps are not directly transferred between devices. For Apps, the transfer process creates a record of the Apps that are installed on the donor iPad - and it is this record of installed Apps that is transferred to the target (new) device. For Apps that are still available for download from the App Store, the corresponding Apps are automatically downloaded and installed from the App Store.

Not all Apps will, necessarily, continue to be available. Apps may have been removed or retired from the App Store by the respective App Developer. Some Apps may have been abandoned - and may not be compatible with the new device. Where a compatible App is not available, you’ll not be able to transfer/install the App.

New iPad - Change AppleID Account

Carefully consider what, if any, sensitive iCloud data should be merged with the AppleID account that you ultimately intend to use with the new iPad. The merge process, once performed, cannot be reversed.

As you wish to change and use an entirely different AppleID with the iPad, first ensure that you have disabled the Activation Lock that will otherwise cause difficulties in the future. You can disable the Activation Lock by disabling the Find My service from iPad/iPhone settings before trying to use a different AppleID account:

Settings > [Your Name / AppleID] > Find My > Find My iPad - set to OFF

Having disabled the Activation lock, you can now sign-out from your old AppleID:

Settings > [Your Name / AppleID] > Sign Out

As you sign out you will have opportunity to delete or keep a local copy of the iCloud data (e.g., Calendar, Contacts, Notes, Keychain Passwords etc.) that relates to the original AppleID. Data that you choose to keep will eventually be merged with the target AppleID; other iCloud data will be wiped from this iPad as you sign-out from iCloud. 

Also ensure that you have signed-out from Messages and FaceTime:

• Settings > Messages > Send and Receive > [AppleID] - scroll to the bottom where you will find your signed-in AppleID highlighted in blue text; tap and select Sign Out

• Settings > FaceTime > [AppleID] - again, scroll down the page to find your signed-in AppleID highlighted in blue text; tap and select Sign Out

After signing out, a restart of your iPad is recommended:

Restart your iPad - Apple Support

After restarting, you can sign-in to your new AppleID account from iPad settings - and also sign-in to Messages and FaceTime if necessary. Any iCloud data that you saved to your device during the previous sign-out will be merged with your new AppleID account.

Apple IDs are intended for a single user account and purchases/downloads cannot be transferred to another ID. They are associated with the Apple ID used when they were purchased.

Once you have it set up with each of you having their own Apple ID account, you can possibly set up family sharing.

Family Sharing - Apple

Part Two

Apps

All Apps that you purchase are forever tied to the AppleID account from which they are purchased.

Apps that remain available - and are compatible with the target device - can be freely downloaded to other devices that are signed-in to iCloud and the App Store with the same AppleID without having to pay again.

If you use a different AppleID, purchased Apps and services will not be directly available to the different account. However, using Family Sharing, it may be possible to share purchased items with up to five other AppleIDs:

Family Sharing - Apple

Set up Family Sharing – Apple Support

Share App Store, iTunes Store and Apple Books purchases with Family Sharing – Apple Support

https://www.imore.com/how-set-up-family-sharing-iphone-ipad

Apps that were downloaded to the old iPad with the old AppleID will still be associated with the old AppleID - and therefore may not update using the new AppleID. This is resolved by offloading or deleting impacted App - and then reinstalling the App(s) from the App Store as required.

Offloading preserves settings and existing files/data associated with the specific App. Deleting an App removes both the App and all associated settings and data/files. As such, consider your intentions for each App that needs to be processed.

This link describes the process to offload an App from your iPad:

https://9to5mac.com/2020/01/21/how-to-offload-apps-in-ios-to-save-space-without-deleting-their-data/

Similarly, the iPad User Guide describes deletion of an App from the iPad:

Remove apps from iPad - Apple Support

Having offloaded or deleted an App from the iPad, simply download Apps that you wish to reinstall from the App Store. These will be associated with the new AppleID; with Family Sharing enabled as previously described, you'll not need to pay again.