You could always try out the 14 day trial, see if the current games (Kick & Fennick and Rogue Legacy) are your thing, or wait for next month to start for other games. If you like it, and have a PS3 or PS4, I highly recommend subscribing to PS+. If you only want PS+ for the saves, you might want to try if it works by backing up saves with the Content Manager. There aren't any games I both have physical and digital, so I can't test anything regarding this.
Anyways, hopefully this'll answer your questions, and give some more information.
To upload saves to the PS+ cloud, you'll only have to do these steps:
1. Tap Content Manager > [Start]
2. Tap [Online Storage]
3. Tap [Online Storage > PS Vita System] or [PS Vita System > Online Storage]
4. Tap a checkbox to set a checkmark for the saved data you want to copy, and then tap [Copy]
Now, each time you play a new game, you'll have to enable online storage for the save.
The saves will of course stay on your memory stick, and online. I'm not sure if there's a certain time that the Vita uploads the saves, but I always back up saves on my laptop, just to be sure.
You can use your PSN wallet to buy PS+. I use Paypal to add money to my wallet, and then buy the PS+ subscription. The prices (in euro, they are probably the same for USD) are 1 month 6,99, 3 months 14,99 and 12 months 49,99. If your subscription is over, you won't be able to use your PS+ games, and presumably saves. If you renew your subscription, everything is back, even the games.
The reason those PS3 and PS4 applications are their own icons, is probably because Sony wants other people to test it out and see what it is, so users get interested and maybe start using it. No idea though, I don't work for Sony
Anyway, I don't think the PS3/PS4 functions need PS+ anyway, like the remote control.
Also, just edit your first post, It might be a huge post, but as long as the text is separated, it's much easier to read.