As a newbie author, I know the challenges someone would face, but there are very few complaints I can pin point besides basic, commonplace errors.
Style: While the excerpts in parenthesis do seem redundant as it is a first person view, where almost everything can be taken as what comes from the MC Heller's mind; they do not detract from the story in any major fashion. Other minor slips in finding your 'style' seemed to appear with the differing levels of passive voice, but all are well within respectable levels. Definitely an enjoyable read!
Story: I loved it, there is a nice pace and even if people assume it to be slow, looking at the word count it definitely reasonable. I would suggest combining chapters for an average word count of roughly 2k, but as the author it is entirely up to you. Realistically it is just another button to press so I can't complain.
Grammar: Steadily improving from what I've read. Writing is hard. That much most people will understand and tend to more lenient about. No blaring issues that'd stop me from reading.
Character: I like Heller a lot. Tends to be 'softer' than most MC's , but that is a nice change of pace. I just want to see more Wolfram/Mike/Chaos Incarnate (I forgot his Earth name) maybe a side chapter every five or six ones you release instead of having him as a novelty as he stands at the moment. Either way, it won't stop me from reading.
But, seriously screw you. Now I have to reformat my story after reading yours. Readability is significantly better than what I'm used to.
Solid read, but throw a bit more thought in descriptions if possible. Not people; places, things, cultures. Why is the blacksmith scene a taboo, etc. Don't be scared to throw a little wall of text if it's necessary to accurately portray what's floating around in your head. Truthfully, I referring more towards cultural aspects as I haven't met much of it and your story has an insane potential to be a leader in that regard.
All the best, Ambush.