Thanks for the additional kind words :)
When the character windows are opened I'm working on putting in tabs on the left-side to switch between characters, and tabs at the top to switch between Cards and Upgrades using the same card view. Hopefully that should help alleviate that issue!
I'll have to look into why the upgrades aren't looping properly, that one is definitely a bug. Each upgrade should never be offered twice, and since there aren't enough upgrades currently in-game to handle looping, it should just offer the +MaxHP upgrade when it runs out for now.
Currently the Engineer isn't in-game yet, so there's no progress to be lost :X The next patch is making the final changes to core systems (card removals and viruses are getting reworked) and filling out the remainder of the core cards for the Soldier and Ninja. The Engineer will likely be next, so she should be playable sometime in early October.
If you're interested in keeping up with things and providing more feedback Discord is a great place for it, and sometimes other people will chime in with their thoughts, too! If you want to join here's a link, and if not that's cool, too. Thanks again!