IS 128GB of storage enough

Yes, as long as the apps have iPad versions available. Not all apps are optimized for iPad, but the vast majority are. You can actually set up your new iPad from the backup of your iPhone. Your iPhone will need to be on iOS 13.4 in order to do that however.

Here's a link on how to set up a new device from the backup of another device --> Set up your iPhone, iPad, or iPod touch - Apple Support

If you don't need to store copious photos, documents, music or files and you're only using 50 GB on your iPhone, it should be fine. Personally, given that memory can't be added after the fact, it's advisable to get the most storage you can afford.

Apparently 128 GBs iPad for me was not enough space.

I tend to use up the iPad storage space that I purchase.

I have quite a few apps and 30 GBs of images on my 128 GBs iPad Pro.

I am thinking about removing all of my images as I have them backed up on my iMac several times over, as well as, backed up to Google Drive/Photos, but I enjoy have instant access to these images right on my iPad.

I keep thinning these images out, though, to try and gain more data storage space on my 2015/2016 iPad Pro.

I, also, have drawings and a plethora of notes, PDFs, documents and other sketches on my iPad Pro.

My 2015/2016 iPad Pro has approx. 22.5 GBs of internal storage left out of 124.5 GBs.

I am contemplating a purchase of a Apple refurbished 2017, 12.9 inch screen iPad Pro with either 256 or 512 GBs because the pricing for a 12.9 inch screen in an older iPad Pro is a whole lot more reasonable and I do not have to purchase any new accessories other than maybe a new 1st gen Apple Pencil.

I refuse to go back to a smaller screen size because of cost constraints associated with of the newest iPad Pro models.

All of our iOS devices (iPhone and iPad) are 256 GB. I don't use the vast majority of the memory, but prefer to have it available if I did need it. In terms of photos, they're all stored on my SSD, my laptop, Google Photos, Amazon Photos and eventually, removed from the iPad except those we feel we need directly on the device. In terms of apps, I have something well over a hundred apps. I don't actually need to keep many files or documents on my iPad as I have everything safely backed up to Carbonite as well.

I do all of this, too, but, for some reason, I like having the equivalent of an organised, easy to access huge image library of images of things that interest me.

Like a a lot of abstract art, automotive art, my own auto art, aircraft art, my huge Star Trek art and image reference library, even my own Trek created art, other Sci-Fi series art.

My “in iPad” image library is very large and highly origanised.

I only have an WiFi ONLY iPad Pro so gaining access to my Google Drive to review images with others can be problematic without access to a WiFi network.

Hence why I have such a large image library on my iPad.

I get that. I think most of us have completely different ways we use our iPad's. I do more work on mine. I do photo editing more on my 4K Ultra Laptop. I can't draw, even stick figures, so even though I have Apple Pencil 2 for iPad Pro 11 and a pencil for my laptop as well, they are more used as pointers than anything else.

You're welcome and enjoy the new iPad when you get it!