Hey OrthelloDev! Getting positive feedback from another RPG dev is always nice. I'm glad you were able to give it a few playthroughs and that you made it reasonably far in! To answer your questions:
Your base chance to hit is 65 (60 natural and 5 Attack rating you get from starting stats). It usually reaches 70 from the base sword, but enemies have their own dodge chances or + to hit modifiers, although all enemies from level 1 have none. Barrels have (I think?) a 9/10 chance to hit - I think the chance to miss them is important since it gives a non-threatening way to establish that attacks miss and miss often.
Right now there are 3 bosses and 4 "unique" mobs scattered around 7 levels (with one of them being a secret level). It would take about 90 mins of playing time for someone with experience to 100% it, so I don't expect most DD players to make it past the Bloodguard boss. Right now I'm satisfied with that length for a game like this, so I'm working on getting everything smooth and polished. Currently I'm working on that shader I mentioned on twitter, and doing some engine shenanigans to improve the lighting. After that there's some as of now secret combat changes to help alleviate boredom non-Diablo-clone fans might experience that'll still stay in the spirit of ARPGs. Hopefully it'll be a nice experience for revisiting players next DD!
Thanks again for the interest and I hope to see your game again next DD - I am envious of your UI work