Can I fully replace my Mac with an iPad, or what key features would I lose?

your list seem to be on spot so if you can live without those

then you could manage

apart from if your iPad would be disabled it would require a computer to restore it.

Since you talk about possibly giving your existing Mac to your grandkids:

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

psmyth wrote:

- I can’t make local backups  of the iPhone or iPad on iPad. On Mac I’ve found these better for restoring than iCloud or QuickStart.

You made this point twice - once when discussing Time Machine backups as well as above. That is incorrect. You may back up your iPad to a Mac or PC.

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

However, backing up your iPad to a Mac or PC requires that you own a Mac or PC. You discuss giving away the Mac…

For the most part, Macs are better machines for content creation than iPads are. There might be particular cases where the iPad has an advantage (e.g., painting applications where you "draw" directly on screen using a "pencil'), but the hardware, operating system, and user interface of the Mac are more oriented towards "serious work".

I'm not trying to dismiss the iPad here. Today's iPads are much more powerful than many personal computers "of old" (including many Macs) were, and anyone who dismisses them as toys would be making the same mistakes as those who dismissed personal computers as toys, based upon the capabilities of the Apple II, TRS-80 Model I, etc. That dismissal was the downfall of many a minicomputer company. But at the same time that iPads have evolved, Macs have evolved, too.

It sounds like you have already thought about some of the tradeoffs that you would need to make in your particular use case.

One thing that is unclear to me is whether you already own the iPad – or are merely thinking about buying an iPad. If you're just thinking about buying the iPad, you could consider purchasing a second Mac, transferring your stuff over to it, then giving the old one to the grandkids.