You can manipulate which inventory expansion appears in the shop. The game picks the one that will free up the most space in your inventory, so just drop some stuff at boss level depth so the type of items you have most of are the targeted.

Normal weapon damage doesn't increase with surprise attacks. It's this way only with dirk and assassin blade. But yes, lunging through doors is still useful.

I don't see that written in the ability description

Lunge always hits, so there is no need to add a surprise attack

Okay, I will use direct messages with possible future bug reports. I just saw others doing it this way as well, didn't know what was better.