Setting up a new ipad without wiping old one

Presumably your new iPad is also a WiFi+Cellular model. If so, you should be able to simply transfer your Cellular service plan by moving your existing DataSIM from your old to new iPad:

Remove or switch the SIM card in your iPad - Apple Support

Should you wish to do so, you can “transfer” (actually copy) all your existing data and settings from your old to new iPad.

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 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

It shouldn’t make any difference whether you move the SIM card before you start - or when you have otherwise finished. That said, I have always moved the SIM prior to starting the process - while the iPad is shut down.