I don't have all that much time atm to write anything (maybe Friday), and also beware, I don't play guitar so you'd have to adjust fingerings yourself.
I absence of any immediate help, here's a few suggestions:
A cool Bodom-style intro to the song. I suggest you don't lose the lower parts of the chords in the keys after measure 18.
Here's one way to take it from here - write a verse riff starting 30. It's probably best to not re-use the same one as intro, but make something new. A simple repeating chord progression would work just fine (I was thinking something like D-B-F-C; D-B-F-G - cliche but practical; you could also build on the progression you used in keys earlier but give that to guitars). Once that's out of the way, you may or may not want to add extra "frills" to it. Most of the "unfinished" feeling will likely be covered up by vocals later on.
Then, some sort of "intermission". Probably a heavy "headbanging" riff. A short guitar run and transition back to verse.
Verse again.
After that, transition and chorus (some variation of intro riff).
Then, any sort of cool bridge and back with an instrumental section, possibly a solo. Transition back to the original chord progression or similar, in background with a funky guitar solo. Write something that you think not only sounds cool, but is also within your skill range to play
Back to chorus. Then maybe a repeat of chorus, with an intensified riff. Short outro.
There's of course numerous ways to do it differently. This is how I've noticed most recent bodom songs, or other generic melodeath songs of similar style usually go.