Motorola G2 Issues

Hi Folks,

I've got an old motorola g2 that i'm trying to get going for a mate who's in need of a phone but doesn't have the cash to buy anything atm.

Tried to sort it this morning but having some problems that I could do with help with if possible. They are:

It's refusing to download or install any apps or update the existing apps, i've got it to download the latest version of the google play store but still nowt.

The micro sd card I stuck in was rejected although after formatting it now seems fine.

Screen is cracked at the top & a hairline crack at the bottom edge, wondering whether to replace it which i've had priced at about 50 quid or is it just worth sticking a screen protector over it to protect from further damage?

Apart from the few niggles mentioned above it works perfectly, still a decent phone to use & reasonably quick. It's a bit held back as i've been told it isn't possible to upgrade from android 6.0 to 7 unless there's a way to download android 7 then manually install.

Any help greatly received.
Luke