Wow - what a story! It sounds like you're writing an epic, and I'd love to help out with the editing process. I'm an Australian commercial lawyer, so the English language is my bread and butter. That being said, I'm also an avid reader of fantasy and adventure novels, so I'm well-versed with the genre.
If you aren't after critique or commentary, I respect that. It's your work, you've poured your heart and soul in to it; I'm not about to come in and tell you what your soul should look like. I can, however, proofread it for, as you say, grammar, punctuation and spelling. When we get to editing for things like flow, clarity, etc. we'd be tiptoeing a pretty fine line between proofreading and re-writing, so I'd essentially give you my thoughts on it and you could make the call from there. For anything other than minor punctuation/spelling corrections, I'd be seeking your approval first.
If it's in word form, I'll do the whole thing tracked so you can see exactly where and what I've edited. The rate and timeline I've quoted is due to the length of the novel, and the fact that the process would likely require multiple readings. However, if you're interested in working together, let me know via chat and we'll work out the details with a little more specificity. If not, good luck! It sounds like an epic undertaking.
Kind Regards,
Kristian.