2 geeky questions for you ...

[nappyaddict]

My first one is whether Google+ backs up things like your memos/text messages. I know it backs up photos and phone contacts. If not is there an app that can do that? When I had an Iphone the Icloud app did this automatically.

My other one is how to tether my Samsung Galaxy Ace 2 as a mobile hotspot for my Nook Tablet.

Not sure about Google+ as I uninstalled that.

On Android, there is SMS Backup+ which will backup your text messages to Gmail.

Not sure about Galaxy Ace 2 but on the Galaxy Ace, Hotspot is found under Settings, Wireless, Tethering, Portable Wi-Fi Hotspot

is it possible to change the portable wifi hotspot password?

Yes, when you set up the hotspot it needs a password.
It may prompt that each time it is setup, or there may be a menu option for setting the password.

Have a look through the setttings on your phone, it should be fairly self explanatory.

I am not sure on the difference between a hotspot and tethering... some providers charge extra for allowing tethering.

Example: Three - tethering/hotspot policy