Re: Matrix of offline wallet Armory versions and compatible with current Armory vers

I think you're safe from 0.91 onwards, for now:

1.) If I'm using v. 0.90 as my offline wallet and don't want to upgrade, do I need to use an older version of Armory for my online wallet?

0.91 at best. You should upgrade, at least to get the security and bug fixes.