I am not able to get text messages on my iPad. I followed the steps above but cannot add my phone number

You can only do iMessage on an iPad, unless you have an iPhone. If you have an iPhone, then you would need to set the iPhone up for Text Message forwarding. Text messages require a cellular connection. See this to set the iPad up to use the iPhone for SMS. How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support

Do you have an iPhone - or just an iPad?

An iPad, whether a Cellular model or not, is not capable of directly accessing Cellular Voice or SMS/MMS Messaging features. An iPad with either WiFi or Cellular connectivity alone can only access IP-data services.

However, If paired with an iPhone, the capabilities of iPad significantly broaden to include access to Cellular Voice and Messaging services of the associated iPhone - relayed to the iPad over WiFi using Apple’s continuity features.

More information about Continuity and the relevant Cellular services can be found here:

Continuity

Use Continuity to connect your Mac, iPhone, iPad, iPod touch and Apple Watch – Apple Support

SMS/MMS Messaging

How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support

WiFi Calling

Make a call with Wi-Fi Calling – Apple Support

If you have an iPhone - and both iPad and iPhone are signed-in to iCloud with the same AppleID, to send SMS/MMS messages from your iPad you must explicitly enable Text Message Forwarding for your iPad on your iPhone...

On your iPhone:

Settings > Messages > Text Message Forwarding - set to ON - and explicitly enable your iPad from the list of devices.

Also ensure that Messages in iCloud is enabled on both your iPhone and iPad:

Settings > [Your Name / AppleID] > Messages - set to ON

I have my iPhone and iPads set up to enable me to communicate via the iPad through iMessage with my Android user friends. I've got a group text going that started in 2018. This past weekend after I upgraded my iPad to iOS 14.4, I am no longer able to send or receive messages to that group on my iPad; only on my phone.

If it's just a wifi iPad, you don't use a phone number in messages, you use your Apple ID.