over 2 years ago - AndrewT - Direct link
In all honesty I'm not sure; I know Steam Cloud sync needs to be enabled but I can't really test whether the overlay needs to be.

The other question is whether it needs to be active once the purchase is made. I suspect not! So perhaps you could enable it to buy the subscription (either yourself or with help), then disable it to play.

Not a very definite answer I know, I'm sorry!  
over 2 years ago - AndrewT - Direct link
I'm very glad to hear that!

All the best!