500GB is enough for this gen. And 1TB isn't enough for this gen.

If that makes sense.

When I delete a game from my PS4, will the memory data get deleted too? 

I expect to mostly still buy physical and really only download PSN+ "free" games and indies. I was sorely tempted to buy Bloodborne off PSN with it being at a considerable discount. But just the thought of downloading 27GB at our internet speeds is offputting. So I will wait a bit more to get Bloodborne physical a bit later.

So for me I think a 1TB HDD will be enough, even if some game data management will be needed. I expect for the most part it would mean juggling the game data for physical game installs, and I would be able to leave the downloaded games alone.

Unfortunately I only have a 500GB and I haven't looked into the whole external HDD back up and replace HDD thing. When last I tried to back up my PS3 HDD I got hit with copyright prohibitions which means I could not back up my PS3 HDD properly, and I gave up the idea of putting in bigger HDD on my PS3. I assume the same copyright restrictions will apply to backing up a PS4 HDD, which makes HDD swapping a bit annoying. Pretty dumb when Xb one and Wii U both allow external game storage and streaming from the external HDD.

No, you'd have to manually delete you saved game data for a game.

I still have my saved game data for The Walking Dead games, even though they're not installed on my PS4 anymore.

THIS IS AWESOME!!!

I have a 1TB drive in my PS4 since launch, I've been getting only digital games, and 20 months later I still have 600GB free space.
When I'm done with the game, it gets deleted. In the off chance that I will decide to replay it 3 years later, I'll just download it again. It doesn't take long to do it, it's done while I'm sleeping anyway.

nope 1tb is way to small. on my xbone i have a 3tb hard drive and i already used up more then 1tb of that , in addition to 500gb harddrive

I've been uninstalling games for over a year on my ps4. 1TB won't make a lot of difference.
But I don't need old game data to stay on the hdd. I buy physical and installation is very fast if I ever want to play it again. Usually keeping my screenshots is enough to scratch that itch of 'What was that game like'. No time to replay games unfortunately.

Yes it will fill up quick. Because of all the bloody patches we need this gen more so than last, deleting games will be kind of meaningless cause come end of gen those patches may not be available again and then you got a useless game disc sitting in your collection.

Nope